ASSESSMENT OF ANALOGIES USED IN PRESENTING GENETICS IN SENIOR SECONDARY SCHOOL BIOLOGY TEXTBOOKS IN OSUN STATE OLUSEUN ESTHER OYINWOLA EDP16/17/H/0221 CHAPTER ONE INTRODUCTION Background to the Study Science is a system of acquiring knowledge based on scientific method

ASSESSMENT OF ANALOGIES USED IN PRESENTING GENETICS IN SENIOR SECONDARY SCHOOL BIOLOGY TEXTBOOKS IN OSUN STATE
OLUSEUN ESTHER OYINWOLA
EDP16/17/H/0221
CHAPTER ONE
INTRODUCTION
Background to the Study
Science is a system of acquiring knowledge based on scientific method, as well as to the organised body of knowledge gained through such research (Rocard, 2007). According to Farabee (2002), science as an objective, logical, and repeatable attempt to understand the principles and forces operating in the natural universe. It is from the Latin word, scientia, meaning, ‘to know’ (Farabee, 2002). It is a great enterprise which nations depend on, in order to advance technologically. Therefore, science is receiving much emphasis in education because of its significance and relevance to life and society (Ghumdia, 2016).

One very important way of knowing, discovering and understanding is through science (Abell, 1994). This is because science concerns itself with questions which can be answered by reproducible measurements or abilities to ask questions and to get answers, which can be interpreted and built up into a corpus of meaningful knowledge. Hence, we do science to make sense of our surroundings (Chu, 2008). As a field of study, science has many compartments, which are basically known as its branches. One of these many branches is the natural sciences, which stipulate that knowledge must be based on observable phenomena and must be capable of being verified by other researchers working under the same conditions (Popper, 2002).

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From this natural science, we have biology that concerns itself with the study of life and living things, including the laws that govern the phenomena of life (Ramalingan, 2010). According to Sorajini (2009), the term biology is defined as the study of living things interacting with its non-living components. This is why Agogo and Naakaa (2014) are of the opinion that biology is a fascinating study that ranges from microscopic cellular molecules to the biosphere, encompassing the earth’s surface and its living organisms.

Biology is a huge subject (Griffiths, Gelbart, Miller, ; Lewontin, 1999). The planet Earth contains a staggering array of life-forms. Already we know about the existence of 286,000 species of flowering plants, 500,000 species of fungi, and 750,000 species of insects (Griffiths et al, 1999). In addition, many more species are still being discovered. Fifty years ago, the science of biology was divided into separate disciplines, each analysing life at a different level. There was morphology, physiology, biochemistry, taxonomy, ecology, genetics, and so on, all working largely in separate academic compartments (Ramalingan, 2010). However, discoveries in genetics have provided some of the most important unifying themes for the whole of biology, so that now conceptual threads link the subdisciplines (Griffiths et al, 1999).

Genetics is the study of genes, genetic variation, and heredity in living organisms (Griffiths, Miller, Suzuki et al. 2000). According to Chattopadhyay (2017), almost 100 years after coining of the terms “genetics” (William Bateson in 1906) and “gene” (Wilhelm Johansen in 1909), the field of genetics has expanded to cover many areas beyond merely the study of inheritance. A good understanding of genetics now requires knowledge about structure and function of the cell and its organelles and of cell division and reproduction (Chattopadhyay, 2017).

The field of genetics is often believed as a subject or a topic in biology that is difficult to learn and comprehend. A review of literature on learning difficulties in genetics is provided to explore the nature of the difficulties, with likely explanations for the difficulties observed (Chu, 2008). Çimer (as cited in Etobro ; Fabinu, 2017) maintained that many concepts or topics in biology, including water transport in plants, protein synthesis, respiration and photosynthesis, gaseous exchange, energy, cells, mitosis and meiosis, organs, physiological processes, hormonal regulation, oxygen transport, genetics, Mendelian genetics, genetic engineering, and the central nervous system can be perceived as difficult to learn by secondary school students. Whereas Tekkaya, Özkan, and Sungur (2001) found that hormones, genes and chromosomes, mitosis and meiosis, the nervous system, and Mendelian genetics were considered difficult concepts by secondary school students.

Indubitably, many would admit that genetics is an important subject to learn in these days and age where its applications are ubiquitous and even the cause of many debates (Chu, 2008). Nevertheless, due to the nature of the subject matter and the way learning processes occur and, perhaps, the way it is being imparted, the understanding of genetics ideas of the majority of students is thought to be very poor and full of misperceptions and alternative views. But, according to Caccavo (2005), man should study genetics for two reasons; to gain intellectual gratification that comes from understanding natural patterns and processes and to apply that understanding to environmental problems that confront mankind. Thus, genetics occupy a central position in biology as well as school curriculum and it plays a very important role in scientific advancement that affects the lives of mankind (Agogo ; Naakaa, 2014).

It is especially difficult for learners to understand and explain most science concepts (genetics), which they are not able to test directly and observe clearly (Thiele ; Treagust quoted in Yener, 2012). This is why Lawson (1993) is of the opinion that analogies can help theoretical concepts of this kind to be stirred in the mind and make them clear. But these analogies can better be cited in a given textbook that explains their usages.
Textbooks are vital parts of instructional materials which cannot be overlooked in teaching and learning process. Nowadays, despite the improvements observed in technology and communication, textbooks retain their importance for students and teachers in classroom environments. Throughout the education process, science and technology textbooks are one of the most commonly used effective teaching materials (Yener, 2012). It is a well-known fact that students and teachers trust and are highly dependent on textbooks (Lumpe ; Scharmann, 1991). Nigerian science teachers rely on textbooks for the appropriate content materials, which satisfy the requirements for the West African Examination Council (WAEC) and the National Examination Council (NECO) syllabi in different science subjects. Therefore, analysis in a variety of ways of the textbooks used by students and teachers will contribute to the literature on science education.
One of the issues that should be analysed in science and technology textbooks is the way analogies are configured by the author(s). To Yener (2012), analogy is mostly used for understanding abstract concepts and complicated issues. An analogy is an explanation that compares a fact that is unknown and unfamiliar with another known and familiar one. The unknown fact is the target while the known fact is the analogue. The analogy compares the similar characteristics of the target and analogue and then a transition from the known information area to the unknown information area is made (Duit, 1991; Harrison ; Treagust, 1994). Hence, it is against this background that this study is designed to assess the analogies used in presenting Genetics in Senior Secondary School Biology Textbooks in Osun State.

Statement of Research Problem
According to Lee (as cited in Maliq, 2012), language plays a vital role in facilitating students in learning science that can provide them a system for thinking and constructing their understanding, along with sharing their ideas. But, it is a well-known fact that science uses technical languages that are different in some cases from everyday language use of the learners. Many students do not do well in science particularly in Biology as a result of the language used in communicating science concepts. Many researchers (Lemke, 1990; Halliday ; Martin, 1993; Fang, 2005; Tan ; Soong, 2006) have identified the teacher’s language use as a barrier to the students’ understanding of science with special emphasis on Biology. Also, there are a number of ways language can make understanding of science more difficult, such as alternative meanings of words, students’ lack of appropriate vocabulary, the specialised vocabulary used by scientists, and the English as a second language (Sullenger, n.d.). Mastropieri and Scruggs (1991) are even of the opinion that there are many researches that have shown that language can interfere with students’ test results and interaction between students and their teachers. This study therefore focuses on the analogies used in presenting genetics in selected Biology textbooks.

Purpose of the Study
The purpose of the study is to assess the analogies used in presenting Genetics in Senior Secondary School Biology Textbooks in Osun State. The specific objectives of this study are to:
identify the analogies used in the presentational format in presenting genetics in selected Biology textbooks;
describe the use of analogies used in the level of enrichment of analogies used in presenting genetics in selected Biology textbooks; and
compare the analogies identified of analogical position in presenting genetics in selected Biology textbooks.

Research Questions
In order to provide answers to the concern of this study, the following research questions were raised:
What are the analogies used in the presentational format in presenting genetics in selected Biology textbooks?
What is the description of the use of analogies used in the level of enrichment of analogies used in presenting genetics in selected Biology textbooks?
How do the analogies identified of analogical position compare in presenting genetics in selected Biology textbooks?
Significance of the StudyThis study is significant as it attempts to assess the analogies used in presenting Genetics in Senior Secondary School Biology Textbooks in Osun State. It will provide basic information on the presentational format, analogy positions and the level of enrichment of analogies used to teach Biology in senior secondary school textbooks in Osun State. The study will also be of benefit to the students of higher institution especially by helping them to identify the analogies used in presenting Genetics in Senior Secondary School Biology textbooks. Moreover, this study will provide a standard by which students will determine how they select biology textbooks in the use of analogies for explaining genetics.
In addition to these, this study will provide a standard by which textbook authors, science teachers, and teachers in training, school administrators and the curriculum developers will describe the use of analogies in presenting genetics in selected Biology textbooks. The future researchers may also use the findings of this study in getting related literature regarding this subject. Finally, it would also be of great value to tertiary institution students researching into similar area. The study would be significant to policymakers and policy implementers, as they would make use of the findings and recommendations of this study.

Scope of the Study
This study is survey research design and focuses on the assessment of analogies used in presenting Genetics in Senior Secondary School Biology Textbooks in Osun State. The scope will be limited to these six selected Biology textbooks: (i) Excellence Biology for Senior Secondary Schools; (ii) Modern Biology for Senior Secondary Schools; (iii) New Biology for Senior Secondary Schools; (iv) Progressive Biology for Senior Secondary Schools; (v) Comprehensive Certificate Biology for Secondary Schools and (vi) Essential Biology for Senior Secondary Schools.

Conceptual Framework
This conceptual framework is envisioned to assist the researcher develop awareness and understanding of the situation under study and communicate it. This section of the work focuses on models that explain the constructs, ideas that are the major variables in the study. Some few selected models on the use of behaviour modification techniques by counsellors or teachers were discussed.

Coding Theory and Biological Information Processing
Battail (1997) argues, similar to Eigen (1993), that for Dawkins’ model of evolution to be tractable, error-correction coding must be present in the genetic replication process. According to Battail (1997), proof-reading, as a result of the error avoidance mechanism suggested by genome replication literature, does not correct errors present in the original genetic message. Only a genetic error correction mechanism can guarantee reliable message regeneration in the presence of errors or mutations due to thermal noise, radioactivity, and cosmic rays (Battail, 1997). The survival of an organism necessitates the existence of a reliable information replication process. Therefore, error correcting codes must be used in replication or in another process of information regeneration that precedes replication. Battail (1997) also claims that genetic information undergoes nested encoding, where the result of a previous encoding process is combined with new information and encoded again. The more important genetic information is assumed to be in the primary coded message (Battail, 1997). Battail’s nested coding model mirrors coding theory’s concept of concatenated codes (Blahut, as cited in May, Vouk, Bitzer, & Rosnick, 2002). Based on Battail and Eigen’s works, the initial communication view of the genetic system proposed by May (1998) is modified as follows:
The replication process represents the error introducing channel; and
Assuming a nested genetic encoder, the genetic decoding process occurs over three levels: transcription, translation initiation, and translation elongation plus termination.
Figure 1 below depicts May et al, (2002)’s final coding theory view of translation initiation. Battail (2000) makes a plea for increased research for the purpose of identifying the error-correcting process proposed Battail (1997). Though there is little-known research into error-correcting models for genetic processes (May, Vouk, Bitzer, & Rosnick, 1999), there is some research into coding theory-based approaches to analysing genetic sequences (Arques & Michel, 1997).

Figure SEQ Figure * ARABIC 1: Modified Coding Theory View of the Central Dogma
Source: May et al, (2002)
Coding Theory and DNA Computing
Kari, Kitto and Thierrin (as cited in May et al, 2002) use circular codes to define heuristics for constructing code words for DNA computing applications. In DNA computing, the information storage capability of DNA is combined with laboratory techniques that manipulate the DNA to perform computations (Kari et al, as cited in May et al, 2002). A key step in DNA computing is encoding the problem in the DNA strand. The challenge is to find code words for encoding that do not form undesirable bonds with itself or other code words used or produced during the computational process. Kari et al (in May et al, 2002) used coding theory to define rules for constructing “good” code words for DNA computing.

Coding Theory in Reading Frame Identification
Arques and Michel (1997) statistically analysed the results of 12,288 autocorrelation functions of protein-coding sequences. Based on the results of the autocorrelation analysis, they identified three sets of circular codes X0, X1, X2 which can be used to distinguish the three possible reading frames in a protein coding sequence (Arques & Michel, 1997). A set of codons X is a circular code, or a code without commas, if the code is able to be read in only one frame without a designated initiation signal (Arques & Michel, 1997). Crick et al (cited in May et al, 2004) originally introduced the concept of codes without commas in the alphabet A, C, G, T. It was later successfully addressed and extracted over the alphabet R, Y, N (Arques & Michel, 1997). Arques and Michel (1997) defined a circular code over the A, C, G, T alphabet. They were able to use the three sets of circular codes to retrieve the correct reading frame for a given protein sequence in a thirteen-base window. They have used their coding-based model to analyse Kozak’s scanning mechanism for eukaryotic translation initiation and other models of translation (Arques ; Michel, 1997).

Coding Theory Based Sequence Analysis
Stambuk also explored circular coding properties of nucleic acid sequences (Nikola, cited in May et al, 2002). His approach was based on the combinatorial necklace model which asks: “How many different necklaces of length m can be made from a bead of q given colours (Elwyn, as cited in May et al, 2002). Using q = A, C, G, T and q = R = Purine, Y = Pyrimidine, N = R or Y, Stambuk applied the necklace model to genetic sequence analysis, enabling the use of coding theory arithmetic in the analysis of the genetic code (Nikola, as cited in May et al, 2002). Although Stambuk did not use error control coding in his analysis, his work provided important insight into the structure of DNA sequences (Nikola, as cited in May et al, 2002).
It is on the premise of the inter-relationships and importance of these variables that this research seeks to assess analogies used in presenting genetics in senior secondary school biology textbooks in the study area.

Operational Definition of TermsThe following terms are defined as they will be used in the study for the purpose of clarity:
Biology: This refers to a natural science which examines living beings and how they interact with one another and their surroundings.

Genetics: is the study of heredity, the process in which a parent passes certain genes onto their children
Heredity: It describes how some traits are passed from parents to their children.

Deoxyribonucleic Acid (DNA): is the molecule that carries all the genetic information of an organism. It can also be thought of as a blueprint containing the instructions that govern the production of proteins and other molecules essential to cell function.

Gene: is the segment of DNA that tells the cell how to make a certain protein.

Analogy: is the process of identifying similarities and differences between two objects or processes or a method of describing things that are known in terms of things that are known, that is, in terms of resemblance so that understanding can be achieved and communication made effective.

Textbooks: are regarded by educators throughout the world as a good source of information for teaching students.

CHAPTER TWO
LITERATURE REVIEW
This chapter reviews relevant literature on the effects of metacognitive training and teaching resources with a view to giving the study a concrete background based on the previous works of eminent scholars. The literature review is organised under the following sub-headings:
Meaning of Genetics
Importance of Genetics in Biology Education
Position of Genetics in Senior School Certificate Examination
Difficulties in the Teaching and Learning of Genetics
Methods and Strategies used in the Teaching of Genetics in Senior Secondary School Biology
Textbooks in Science Education
Various Analogies used in Presenting Genetics in Senior Secondary School Biology Textbooks
Empirical Studies
Appraisal of Literature
Meaning of Genetics
Genetics is the scientific study of inherited variation (Kapiel, 2005). It is one of the most difficult topics in the biology curricula at the secondary school and tertiary levels (Hallden, 1988; Johnstone & Mahmoud, 1980). Genetics as an aspect of Biology is concerned with the study of nature and mechanism of heredity (Akinnubi, Oketayo, Akinwande, & Ifedayo, 2012). Anderson, Fisher and Norman (2002) have defined genetics as the transfer of characteristics of an organism. Thus, genetics is being seen as the biology of heredity (Akinnubi et al, 2012). It is a branch of Biology that deals with the study of heredity and variations, the principle that account for the diversity of organism (Kala, 2012).

According to Griffiths et al (2000), genetics is the study of genes, genetic variation, and heredity in living organisms. It is generally considered a field of biology, but intersects frequently with many other life sciences and is strongly linked with the study of information systems. Genetics is a core concept in general biology study, but it has always been seen as a distinct field of study with its own conceptual parameters (Lewis, Leach, & Wood-Robinson, 2000). Klug, Cummings, and Spencer (2006) defined genetics as the biology of hereditary and variation. Hereditary or inheritance focuses on the transmission of characteristics from one generation to another, hence similarities while variation dwells on the causes of differences among individuals (Ekong, Akpan, Anongo, & Okrikata, 2015). Genetics, therefore attempts to explain the mechanism of two constants that are found in the universe – similarities and differences (Ekong et al, 2015).

The field of genetics has expanded to cover many areas beyond merely the study of inheritance (Longden, 1982). A good understanding of genetics now requires knowledge about structure and function of the cell and its organelles and of cell division and reproduction. Genetics is one of the most difficult subjects in the biology curricula at the primary and secondary school (Hallden, 1988; Kelly & Monger, 1974). As noted by Kala (2012), the understanding of genetics at schools depends very much on the pre-requisite of understanding of genetic concepts like the cell it structures and function among others. A good knowledge of genetics is very important to students of Biology and related courses most especially in their later years of study (Okebukola, 2002). However, many students avoid genetics-related questions in Biology at early secondary.

Genetics as a scientific discipline stemmed from the work of Gregor Mendel in the middle of the 19th century (Winchester, 2010). Mendel suspected that traits were inherited as discrete units, and, although he knew nothing of the physical or chemical nature of genes at the time, his units became the basis for the development of the present understanding of heredity. All present research in genetics can be traced back to Mendel’s discovery of the laws governing the inheritance of traits. The word gene, coined in 1909 by Danish botanist Wilhelm Johannsen, has given genetics its name (Winchester, 2010).

The ‘gene’ concept has been continually evolving ever since it was first formulated by Mendel based on his pea plant experiments (Aivelo & Uitto, 2015). Nowadays, Mendel’s findings on heredity in pea plants are referred to as “the laws of Mendelian inheritance” (Smith & Gericke cited in Aivelo & Uitto, 2015). It should be noted that there is wide conceptual variation in the meaning of the ‘gene’: there is no single definition, but rather a group of loosely connected concepts used in different subfields of biology (Flodin, 2009).

Table SEQ Table * ARABIC 1: Modified table from Flodin (2009) interpreting different meanings of ‘gene’ in the textbook Biology. Source: Campbell & Reece (as cited in Aivelo & Uitto, 2015)
The gene as Synonymous to characteristics within subfield
A trait An allele The gene is a trait with physical place (locus) Mendelian genetics
An information A nucleotide sequence The gene provides instructions, is expressed and regulated Molecular biology
An agent DNA The gene acts or interacts, uses, moves or duplicates Genomics
A regulator DNA The gene controls, directs and defines Developmental biology
A marker An allele The gene can be fixed, added and exists in frequencies Population genetics
The term Genetics has also provided some of the most incisive analytical approaches now being used across the spectrum of the biological disciplines. Foremost is the technique of genetic dissection (Griffiths, Gelbart, Miller, & Lewontin, 1999). In this experimental approach, any structure or process can be picked apart, or “dissected,” by looking at how mutant genes influence it. By studying abnormality, we can deduce the normal case. For example, in the study of the development of adult organisms from a fertilised egg, each mutant gene that produces a developmental abnormality identifies a component in the normal process of development (Griffiths et al., 1999). The genetic dissection of paralysed mutant strains of nematode worms has led to an understanding of the genes that control normal movement. The overall picture of a particular process can be assembled by interrelating all these genetically controlled components (Griffiths et al., 1999).

Genetics is one of the most dynamic research disciplines within the natural sciences. It is a steady accumulation and might be changing in time and open to debate (Durkheim, 1994; Ravetz, 1997). Many genetics concepts require abstract thinking. Unless the student has reached the level of formal operational thinking, he/she will not be able to cope adequately with these ideas (Chu, 2008).

According to Chu (2008), genetics is connected with the occurrence of ideas and concepts on these different levels of thought. Observations of morphological characteristics of living things, such as colours of flowers or the height of humans takes place at the macroscopic level and are accessible to the senses. The appeal to cells, gametes, and nucleus, and chromosomes, DNA, genes and alleles to explain the macroscopic level takes students into the microscopic and molecular level, which is not directly accessible to the senses (Chu, 2008). These are then represented and manipulated by mathematics (ratios and probabilities) which are symbolic (for example, Aa represents an allele; a pair of gene) of what is happening at the microscopic and molecular level, and giving rise to the macroscopic level (Bahar, Johnstone, & Hansell, 1999).

Genetics Areas of Study
According to Winchester (2010), the following are the genetics areas of study: Classical Genetics, Cytogenetics, Microbial Genetics, Molecular Genetics, Genomics, Population Genetics, Behaviour Genetics and Human Genetics. These are discussed below:
Classical Genetics
Classical genetics, which remains the foundation for all other areas in genetics, is concerned primarily with the method by which genetic traits – classified as dominant (always expressed), recessive (subordinate to a dominant trait), intermediate (partially expressed), or polygenic (due to multiple genes) are transmitted in plants and animals. These traits may be sex-linked (resulting from the action of a gene on the sex, or X, chromosome) or autosomal (resulting from the action of a gene on a chromosome other than a sex chromosome). Classical genetics began with Mendel’s study of inheritance in garden peas and continues with studies of inheritance in many different plants and animals. Today, a prime reason for performing classical genetics is for gene discovery – the finding and assembling of a set of genes that affects a biological property of interest.

Cytogenetics
Cytogenetics, the microscopic study of chromosomes, blends the skills of cytologists, who study the structure and activities of cells, with those of geneticists, who study genes. Cytologists discovered chromosomes and the way in which they duplicate and separate during cell division at about the same time that geneticists began to understand the behaviour of genes at the cellular level. The close correlation between the two disciplines led to their combination.

Plant cytogenetics early became an important subdivision of cytogenetics because, as a general rule, plant chromosomes are larger than those of animals. Animal cytogenetics became important after the development of the so-called squash technique, in which entire cells are pressed flat on a piece of glass and observed through a microscope; the human chromosomes were numbered using this technique. Today, there are multiple ways to attach molecular labels to specific genes and chromosomes, as well as to specific RNAs and proteins, that make these molecules easily discernible from other components of cells, thereby greatly facilitating cytogenetics research.

Microbial genetics
Microorganisms were generally ignored by the early geneticists because they are small in size and were thought to lack variable traits and the sexual reproduction necessary for a mixing of genes from different organisms. After it was discovered that microorganisms have many different physical and physiological characteristics that are amenable to study, they became objects of great interest to geneticists because of their small size and the fact that they reproduce much more rapidly than larger organisms. Bacteria became important model organisms in genetic analysis, and many discoveries of general interest in genetics arose from their study. Bacterial genetics is the centre of cloning technology.

Viral genetics is another key part of microbial genetics. The genetics of viruses that attack bacteria were the first to be elucidated. Since then, studies and findings of viral genetics have been applied to viruses pathogenic on plants and animals, including humans. Viruses are also used as vectors (agents that carry and introduce modified genetic material into an organism) in DNA technology.

Molecular genetics
Molecular genetics is the study of the molecular structure of DNA, its cellular activities (including its replication), and its influence in determining the overall makeup of an organism. Molecular genetics relies heavily on genetic engineering (recombinant DNA technology), which can be used to modify organisms by adding foreign DNA, thereby forming transgenic organisms. Since the early 1980s, these techniques have been used extensively in basic biological research and are also fundamental to the biotechnology industry, which is devoted to the manufacture of agricultural and medical products. Transgenesis forms the basis of gene therapy, the attempt to cure genetic disease by addition of normally functioning genes from exogenous sources.

Genomics
The development of the technology to sequence the DNA of whole genomes on a routine basis has given rise to the discipline of genomics, which dominates genetics research today. Genomics is the study of the structure, function, and evolutionary comparison of whole genomes. Genomics has made it possible to study gene function at a broader level, revealing sets of genes that interact to impinge on some biological property of interest to the researcher. Bioinformatics is the computer-based discipline that deals with the analysis of such large sets of biological information, especially as it applies to genomic information.

Population genetics
The study of genes in populations of animals, plants, and microbes provides information on past migrations, evolutionary relationships and extents of mixing among different varieties and species, and methods of adaptation to the environment. Statistical methods are used to analyse gene distributions and chromosomal variations in populations.

Population genetics is based on the mathematics of the frequencies of alleles and of genetic types in populations. For example, the Hardy-Weinberg formula, p2 + 2pq + q2 = 1, predicts the frequency of individuals with the respective homozygous dominant (AA), heterozygous (Aa), and homozygous recessive (aa) genotypes in a randomly mating population. Selection, mutation, and random changes can be incorporated into such mathematical models to explain and predict the course of evolutionary change at the population level. These methods can be used on alleles of known phenotypic effect, such as the recessive allele for albinism, or on DNA segments of any type of known or unknown function.

Human population geneticists have traced the origins and migration and invasion routes of modern humans, Homo sapiens. DNA comparisons between the present peoples on the planet have pointed to an African origin of Homo sapiens. Tracing specific forms of genes has allowed geneticists to deduce probable migration routes out of Africa to the areas colonized today. Similar studies show to what degree present populations have been mixed by recent patterns of travel.

Behaviour Genetics
Another aspect of genetics is the study of the influence of heredity on behaviour. Many aspects of animal behaviour are genetically determined and can therefore be treated as similar to other biological properties. This is the subject material of behaviour genetics, whose goal is to determine which genes control various aspects of behaviour in animals. Human behaviour is difficult to analyse because of the powerful effects of environmental factors, such as culture. Few cases of genetic determination of complex human behaviour are known. Genomics studies provide a useful way to explore the genetic factors involved in complex human traits such as behaviour.

Human genetics
Some geneticists specialise in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the mechanisms of human gene function and malfunction and investigating pharmaceutical and other types of treatments. Since there is a high degree of evolutionary conservation between organisms, research on model organisms—such as bacteria, fungi, and fruit flies (Drosophila)—which are easier to study, often provides important insights into human gene function.

Many single-gene diseases, caused by mutant alleles of a single gene, have been discovered. Two well-characterised single-gene diseases include phenylketonuria (PKU) and Tay-Sachs disease. Other diseases, such as heart disease, schizophrenia, and depression, are thought to have more complex heredity components that involve a number of different genes. These diseases are the focus of a great deal of research that is being carried out today.

Another broad area of activity is clinical genetics, which centres on advising parents of the likelihood of their children being affected by genetic disease caused by mutant genes and abnormal chromosome structure and number. Such genetic counselling is based on examining individual and family medical records and on diagnostic procedures that can detect unexpressed, abnormal forms of genes. Counselling is carried out by physicians with a particular interest in this area or by specially trained nonphysicians.

Importance of Genetics in Biology Education
Genetics is not only considered an important topic in biology education, but it has also become very relevant in everyday life (Knippels, 2002). Coila (2018) identified four different ways in which genetics is very important in Biology education. These are:
Diseases and Treatments: Understanding the genetic basis behind human disease is one of the most important reasons for studying the human genome. While many genetic disorders are not treatable, early diagnosis can help improve the quality of life or even extend the lifespan of sufferers. Current clinical trials on genetic therapies for cystic fibrosis, haemophilia, and other genetic disorders offer the promise of eventual treatments that may give sufferers a life free of symptoms. Diagnostic tests can help couples decide whether to risk passing on specific disease-related genes to their children. Tests assist in vitro fertility doctors to specifically select embryos that do not carry the dangerous gene.

Human History: Studying human DNA and genetics can help scientists better understand where humans came from as a species. It can help elucidate the connections between different groups of people and give historians and anthropologists a clearer picture of historic human migration patterns. In some cases, a person’s genome can give clues to his personal ancestry and help him understand his genealogy. Genetic testing has been used to verify or rule out relatedness of individual persons or populations.

Forensics and Legal Implications: The trial of O.J. Simpson in the 1990s brought to public light the use of human DNA in criminal cases, and the importance of human genetics in forensics has become even more important as techniques have improved. Human genetic information has been used to either match or rule out a suspect’s DNA to biological evidence found at a crime scene, to identify victims and to exonerate convicted individuals using newer genetic methods not available at the time of the initial conviction. Paternity testing is another common legal application of genetic testing.

Genetic Enhancement: Human genetic enhancement is a controversial topic, but research in this area holds some of the biggest promise for future applications. It will require a thorough understanding of human genetics before scientists can alter the human genome at the embryonic level, but once that is achieved, it may mean an end to certain incurable genetic diseases such as Down syndrome, congenital deafness and congenital heart defects. More controversial applications may include altering human DNA to enhance athletic ability, intelligence, or other characteristics.

In another instance, geneticists believe that the methods and techniques of genetics are applicable throughout the spectrum of biological activity, and are as relevant to molecular biology as to population studies (Department of Genetics, n.d.). Some of the basic tools of modern biology (analysis of genomic sequences and bioinformatics) are most intelligently used in the knowledge of the genetic principles that underpin the design and application of the software. At the other end of the spectrum, a knowledge of genetics is fundamental to an understanding of the evolution of populations and species (Department of Genetics, n.d.).

Genetics should be interesting in that it has implications of enormous importance for everyone. However, genetics by its nature is complex, especially at the initial stages of learning (Chu, 2008). Genetics education has become increasingly important with the advent of recombinant DNA technologies and the subsequent emergence and availability of genetically modified food and organisms (GMOs). Issues such as DNA screening, cloning, and GMOs are hotly debated in various countries, including India, where a high level of scientific literacy is needed among the general public to address such issues and give informed consent about uses of the new technologies (Dawson & Schibeci, 2003).

The rapid advances in genetic research, the popularity of the topic and the direct role that genetics plays in human health and reproduction make it a scientific discipline that everyone needs to understand (Maigoro, Nansoh, Pam, & Manji, 2017). From the use of DNA in court cases to the discovery of new therapies for genetic diseases, a thorough understanding of the human genome can have important medical, social and legal impacts. Genetic issues now play a large role in health and public policy (Miller, 1998).

Furthermore, in examining the importance of genetics, Thörne (2012) noted that the ever-increasing knowledge about genetics has become a major influence on many aspects of modern society. New technologies are used in different fields, including archaeology and human history, medicine, prenatal diagnosis, reproductive technology, genetically modified organisms (GMO), criminal investigation, cloning etc. Gene technology is also used in the production of vaccine, even if it is still in the experimental phase, there are attempts to produce vaccines against HIV. Gene therapy is another area within gene technology. All of this might not affect the individual citizen directly, but virtually everyone commonly encounters genetics in some aspects of their lives (Thörne, 2012).

Position of Genetics in Senior School Certificate Examination
Abimbola (1998) investigated the Biology content areas that Biology teachers perceived as important but difficult for them to teach and reasons they gave for their perceptions. He noted that some teachers see some Biology concepts as being too complex for students’ understanding; most especially genetics concepts (Abimbola, 1998). Soyibo (1988a) also researched into the teaching of genetics. In his work on conceptual and instructional difficulties in Ordinary level genetics, the researcher reports that the teaching of genetics and ecology have been neglected in most secondary schools in Nigeria. He goes further to remark that only objective questions were set on genetics between 1973 and 1983 WASC Ordinary Level Biology Examination (Soyibo, 1988a). The nonchalant attitude of all the parties concerned with the teaching and learning of genetics particularly, the teachers could be attributed to the nature and type of genetic questions answered by students from time to time (Soyibo, 1988a).
In the Nigerian secondary school education setting, the causes of students’ low performance in genetics courses are as a result of many prevailing factors such as lack of qualified teaching personnel, abstractive presentation of lessons, verbose terminologies and lack of simplification of concepts among others (Akinnubi et al, 2012). It is therefore not out of place to say that Biology students rated most, if not all the concepts taught in genetics as difficult, which bring about their low performance in genetics courses in the secondary school examination. This agrees with Abimbola (1998) who reports that teachers’ perceived concepts like chromosomes, growth mitosis, probability in genetics, neurone coordination and evolution theories as difficult concepts to teach. It also agrees with Okebukola in Akinnubi et al (2012) that at the secondary school level, about 13 Biology topics are difficult to teach. Furthermore, it agrees with Oyeyemi (1991)’s assertion that students’ conception of genetics is generally poor, which brings about low performance in examinations
A review of the West African Examination Council (WAEC) Chief Examiner’s Report in Biology for the May/June and November/December Examinations (as cited by Ekong et al, 2015) in the last decade yields an insight into the direness of the situation. Remarks such as “students’ poor understanding of certain genetics terms”, “non-familiarities with concepts of genetics”, “poor performance on questions related to Genetics” are among many others used by the WAEC Chief Examiners’ in-charge of Biology to describe the weakness of students in Biology examinations (WAEC 2009 – 2013). The perennially poor and fluctuating performance of students in Biology is a recurrent theme in the same document. Failures in Biology, nay Genetics, means a general shortage of manpower in related fields like Medicine, Agriculture, Industry (Samikwo, 2013) and education (Ekong et al, 2015). This picture is even more depressing when viewed against the backdrop that Biology is the third most registered for subject (after English Language and Mathematics) in the May/June WAEC examinations (WAEC, 2009 – 2015).

Abidoye (2005) found the results of students in Biology Examination conducted by WAEC discouraging. This is shown below in Table 2.
Table SEQ Table * ARABIC 2: The Nation-Wide statistics of performance in Science and related subjects in May/June, 2008-2010 Senior School Certificate Examinations

Source: Statistics Section West African Examination Council (WAEC) Office Yaba, Lagos (2011) in Abimbola ; Abidoye (2013).

The results in table 2 show a decline in students’ performance in years sampled, 2008-2010. The percentage of students that had credits was very low compared to the total entry. In 2008-33.9%, in 2009-28.6% and in 2010-33.9% throughout the examination results, the performance of biology students was always below 60% of the total number students who offered biology in the external examination. In the years 2008, 2009 and 2010. The percentage failures were 38.4%, 35.2% and 38.4%. It could therefore be seen from the table that percentage failure of students’ performance increased yearly. The result above showed are the same for all the senior secondary schools in Nigeria.

Table SEQ Table * ARABIC 3: Performance of Candidates in SSCE Science, including Biology

Source: National Examination Council, 2001-2006 Annual Report (cited in Agboghoroma ; Oyovwi, 2015)
From the table above, results of the National Examination Council (NECO) from 2001-2006 showed that the performance of students in Biology has not been encouraging. Okafor and Okeke (2006) noted that students’ lack of understanding of difficult concepts in Biology results in poor performance of students at SSCE and backwardness in scientific and technological advancement of our nation. Also, Umeh (2002) revealed that the nonchalant attitude of students and teachers in the Senior Secondary Schools towards certain concepts in the Biology curriculum are also responsible for poor performance. But, Agboghoroma and Oyovwi (2015) were very emphatic in their assertion that in spite of effort through research on strategies to improve performance in Biology, the WAEC chief examiners annual reports have continued to highlight students’ weakness in answering questions relating to difficult concepts in the areas such as of Genetics, Ecology and Evolution. This shows that genetics in Biology examination has been one topic that is too difficult for candidates to answer, and this has affected the whole performance of students in the general subject (Biology).

Also, Çimer in Etobro and Fabinu (2017) argued that many concepts or topics in biology, including cells, mitosis and meiosis, organs, physiological processes, hormonal regulation, genetics, Mendelian genetics, genetic engineering, and the central nervous system can be perceived as difficult to learn by secondary school students, and these usually affect students’ performance at the senior secondary school examination. Whereas Tekkaya, Özkan, and Sungur (2001) found that hormones, genes and chromosomes, mitosis and meiosis, the nervous system, and Mendelian genetics were considered difficult concepts by secondary school students, which have also affected the examination results.
Difficulties in the Teaching and Learning of Genetics
Learners have difficulties understanding genetics because the terms used in genetics have no common usage outside the genetics classroom (Woody & Himelblau, 2013). For example, terms like heterozygote or genotype, allele or locus are used. Learning genetics is like learning a foreign language. Many terms in genetics are defined in opposition to similar sounding terms whose meanings are quite distinct. For example, heterozygous and homozygous, if a student does not understand one of these paired terms, the student cannot understand the other (Woody & Himelblau, 2013). The use of analogy can help learners to understand the vocabulary of genetics. For example, loci and genes can be explained using the analogy of street addresses.

The complex nature of genetics is another reason why genetics is difficult to learn and teach (Bahar, Johnstone & Hansell, 1999). The structure of the knowledge of genetics is complex and students have to use this complex knowledge in solving complex genetics tasks (Collins & Stewart, 1989). According to Wood-Robinson (1994), young people use their own intuitive ideas to explain some aspects of inheritance, even before they receive tuition on these subjects. By the time a child receives formal science education, his/her preconceptions are already well-established working theories, and difficulties arise when these ‘naive’ theories disagree with the presented science concepts in the classroom. These preconceptions then inhibit new learning and lead to the establishment of misconceptions or alternative conceptions (Arnaudin & Mintzes, 1985). In the opinion of Driver and Bell (1986), these can be very stable and highly resistant to change. Obviously, even Wood-Robinson (1994) believes these ideas should be considered by teachers when planning and teaching; if they are not, and if they are erroneous, they can easily interfere with the acquisition of scientifically acceptable knowledge about genetics.

Nonetheless, Knippels (2002) asserted that there are several factors that contribute to the difficulties in implementation of active forms of learning. Firstly, students are not always willing to spend time and energy on gaining new learning skills. Secondly, teachers do not always see the benefits, they may feel it is time-consuming, or they may find it hard to coordinate and/or difficult to lose their autonomy. In addition, teachers often think that active learning is not appropriate for their subject matter. Finally, school management and organisation are not always equipped for active learning forms as self-study hours, etc (Knippels, 2002).

Difficulties that students encounter in solving Mendelian genetics problems may be associated within the cognitive development levels of students. Various studies (Walker, Hendrix, & Mertens, 1980; Gipson, Abraham, & Renner, 1989) originating from a Piagetian framework, indicate that secondary school students are lacking from formal reasoning skills needed to solve genetics problems.

Also, Knippels (2008) argued that there is a cognitive view to the difficulties of learning and teaching of genetics. She is of the opinion that the ‘expert-novice’ approach is characteristic for the cognitive framework in genetics education. By comparing the problem-solving performances of experts and novices (successful vs. unsuccessful), researchers try to characterise cognitive differences between these two groups. Though, there are many works of scholars (See Knippels, 2008) that focused on characteristics of successful and unsuccessful problem-solvers in the context of genetics, like identification of heuristics and key issues in experts’ reasoning, nonetheless, practical applications are very limited since there is a big difference between the aspirations of experts and the novices. According to Collins and Genter (1987), experts often spent a large chunk of time in acquiring knowledge and artificial mental models of their domain. These experts works are usually carried out in a specialised place, like laboratories, for such endeavour and not in classroom settings. Thus, Knippels (2008) noted that the cognitive perspective does not primarily focus on genetics: the context of genetics is used to test general problem-solving skills.

In another instance, Hallden (1988) pointed out that when genetics is taught at the macroscopic level, students are able to understand what they have been taught. However, when they move to the molecular level, they often fail to grasp the connection between ‘genetic materials’ and ‘genetic traits’, and new concepts (at the micro-levels) appear to be meaningless words. Also, Stewart (1983) provides another example of the same confusion, noting that it is difficult for students to grasp the connection between meiosis (micro-levels) and Mendelian genetics (macroscopic level).

On the issue of difficulty in relation to time, Boersma (as cited in Chu, 2008) introduced the ‘level-matrix’, which consists of levels of biological organisation (vertically) and knowledge levels (horizontally) and is designed to develop subject matter sequences. A sequence starts in the cell of the matrix that is defined by the organisational level and the first knowledge level. From there on, it is prescribed to move horizontally (ascending or descending to a next level of biological organisation), or vertically (to a next knowledge level) to an adjacent cell. This procedure can be repeated as long as necessary. However, this was not easy to achieve, mainly because of inadequate time allowance in school.

According to Chu (2008), some researchers are of the opinion that one of the causes that makes genetics to be so difficult is because several levels of organisation must be integrated in order to understand the processes underlying genetic phenomena and to grasp the overall picture of inheritance and genetics. It means that to understand genetics fully, it is necessary to experience all the above four levels. Thus, according to the information processing model, this may pose problems because the working memory has a limited capacity. Using several levels simultaneously is likely to bring about an information overload Chu (2008).

There is also the difficulty in the topic sequence as given by many biology textbooks. The research that was carried out by Cho, Kahle and Nordland (1985) on three most widely used biology school textbooks in America and inferred that the organisation of the concepts is inadequate. In this particular study, the three textbooks discussed meiosis before genetics and treated the two as separate topics. Moreover, the topic of meiosis was isolated from that of heredity. One concern about this sequence is that since meiosis is involved in the separation of alleles during sexual reproduction and genetics concerns itself with the tracing of alleles from parents to offspring, these two concepts should not be separated in these textbooks but the relationship between them should be explicitly done (See Tolman, 1982). More so, there is the difficulty in which of the topics should come first, either meiosis or genetics or vice-versa (See Ausubel, Novak, ; Hanesian, 1978; Tolman, 1982).
Methods and Strategies used in the Teaching of Genetics in Senior Secondary School Biology
Genetics as a topic in senior secondary school biology is being taught just like every other topic at the secondary level in Nigeria. As noted earlier that genetics is a difficult topic to treat in biology, this means that teaching this field of biology would involve different teaching methods and strategies. As there are many teachers, so there are many methods and strategies for teaching genetics. No matter the teacher’s level of qualification, he/she must master the use of certain methods and strategies for effective teaching and learning to take place in his or her class. Thus, this segment takes a cursory look at the different methods and strategies employed in the teaching of genetics in Nigerian senior secondary schools.

Instructional strategies
Instructional strategies are techniques teachers use to help students become independent, strategic learners. Marboro (2012) emphasised that strategies become learning strategies when students independently select the appropriate ones and use them effectively to accomplish tasks or meet goals. He further explained that instructional strategies can:
motivate students and help them focus attention;
organise information for understanding and remembering; and
monitor and assess learning.
Marboro (2012) opined that to become successful strategic learners, students need:
step-by-step strategy instruction;
a variety of instructional approaches and learning materials;
appropriate support that includes modelling, guided practice and independent practice;
opportunities to transfer skills and ideas from one situation to another;
meaningful connections between skills and ideas, and real-life situations;
opportunities to be independent and show what they know;
encouragement to self-monitor and self-correct; and
tools for reflecting on and assessing own learning.

Instructional strategies shape the lesson environment. An effective teacher chooses a teaching strategy or a set of strategies that will engage the students or learners.

Lecture Method
Lecture method can be regarded as a process whereby the teacher delivers verbally a prepared body of knowledge to his students who listen and jot down points from the teacher (Azuka, Durojaiye, Okwuoza, & Jekayinfa, 2013). The lecture method to the teaching of genetics in senior secondary school is teacher-dominated or teacher-centred approach to teaching (Okoli, 2006). It involves the teacher telling the students what he or she knows about a concept. Most of the talking is carried out by the teacher while students remain as passive listeners taking down notes. Hence, it is referred to as didactic approach or talk-chalk method (Nwagbo, 2001, 2006). It is basically a teacher-centred approach which encourages one-way communication, though it can be used to communicate to a large crowd of students orally or through electronic media like radio or television (Azuka et al, 2013).

Most teachings carried out in our schools today are through the use of the lecture method (NOUN, n.d.). This is because large amount of information can be presented to students in a limited time. Most teachers embrace the use of this method due to the fact that it leads to fast coverage of the syllabus and this is being used to teach genetics in the secondary schools in the country. In addition to that, the lecture method can be used to teach large and small class sizes. The teacher may ask few or no questions in the process. It does not require the use of instructional materials or resources (Okoli, 2006). To this effect, the students are denied the opportunity to develop manipulative skills.

According to Ametefe (2012), the lecture method is mainly used to build upon the learners’ existing base of knowledge. Thus, while beginning a lecture, it is essential to cite the lecture at the learners’ level. This can be done by asking some relevant questions and starting straight away (Ametefe, 2012). Thereafter, the trainer will have to make constant efforts to situate the new information in the content of the learner by continuously providing examples and illustrations to relate to the learners’ content (Ametefe, 2012). Other advantages of the lecture method that are stated by the National Open University of Nigeria (NOUN, n.d.) include: less time-consuming in the part of the teacher in preparation for his/her lessons since no materials are needed in the process; it is cheap to operate; it is a good method of delivering large amount of knowledge in a short time, that is, it leads to a very high content coverage; large size classes can be handled easily; it can be used to introduce new topics; and it helps to develop confidence in his/her teaching as a facilitator of knowledge. The use of lecture method entails a one-way flow of communication from the teacher to the students. It is a teacher-dominated approach (NOUN, n.d.).

Lecture method is often used to deliver a large amount of information to the students in a short period (Berry, 2008). But to Bok (2006), an average student only retains 42% of what he or she learned after the end of the lecture and 20% one week later. This is because the method concentrates on information rather than learners (Al-Rawi, 2013). Thus, just as Aina, and Langenhoven (2015) had noted that students’ retention in a lecture-based science courses is weak, the way this is being done in the teaching of genetics is also not equal to the task of adequately enhancing students’ knowledge on genetics.
Demonstration Method
Demonstration teaching method is a useful method of teaching because it improves students’ understanding and retention (McKee, Williamson, & Ruebush, 2007). This method is a demonstration of doing and showing. The method applies sight and touch rather than hearing as the major means of communication (NOUN, n.d.). According to Al-Rawi (2013), the demonstration is effective in teaching skills of using tools and laboratory experiment in science. However, the time available to perform this demonstration is very limited in a classroom setting. Therefore, a demonstration often designed to allow students to make observations rather than through hands-on laboratory (McKee et al, 2007).

Demonstration method combines telling, showing and doing for the benefit of the students. This method is essential in arriving at fundamental skills and practice in a very short time (NOUN, n.d.). It is the basic method for introducing new skills to students and for developing understanding. It is also basic in getting students accept new and better ways of doing something. Also, the demonstration is always done by the teacher while the students watch. At the same time the teacher does the explanation. In many subjects, the demonstration method appears to be the only possible means of achieving the objectives of learning by doing (NOUN, n.d.).

Eclectic Method
This is a general method which tends to cut across subject boundaries and which can help realise the general objectives of education (Osakinle, Onijigin, & Falana, 2010). The eclectic method is a combination of all that is good in all the other methods of teaching (Osakinle et al, 2010). In a teaching procedure, most students are actively following the teachers’ instructions, observing, asking and answering questions. If, on the other hand, the teacher has done all the talking, he or she is likely to render the learners passive. That means student would not be able to actively take part in the discussion. It is very likely that most learners will forget what they have been taught but they are likely to remember for a long time what they have manipulated or talked about (Obanya, 1980).

Guided Inquiry Method
As the name implies, guided inquiry method is a method of teaching in which students are guided by the teacher to find facts for themselves (Ugwuadu, 2010). It is student-centred, and activity-oriented (Akuma, 2005). According to Fatokun and Yalams (cited in Ugwuadu, 2010), this method helps to increase the degree of students’ interest, confidence, innovativeness, problem – solving ability and consequently improve their performance in both theory and practice. The guided inquiry method also helps students to engage in relatively sophisticated mental processes like formulating problems for investigation, formulating hypotheses, designing experiments, synthesizing knowledge, possessing scientific attitudes etc. (Abdullahi, 1982).

Textbooks in Science Education
Textbooks are important teaching materials that serve as a source for students learning in order to realise the purpose of teaching (Dikmenli, 2015). The textbook is the most widely used of all teaching aids. Few teachers would attempt to teach a course without one (Eltinge, 1988). As a dominant instructional material in science education, science textbooks have determined the content of instruction and teaching procedures in thousands of classrooms for decades (Wang, 1998; Chiappetta & Fillman, 2007). Textbooks provide the foundation for the content of the lesson and represent what is important on a particular topic. In this regard, textbooks should reflect the reform of the curriculum and align with the curriculum requirements (Gök, 2012).
According to Ball and Feiman-Nemser (1988), textbooks are among the major determinants of the knowledge taught in schools. Besides forming a resource for teachers and learners for the subject, textbooks also enable absentees to cover the work they have missed and give students opportunity to revise the subjects taught in lessons according to their learning speed (Küçükahmet as cited in Gök, 2012). Since the textbook reflects the requirements of the curriculum, it also helps to achieve the desired objectives. These features make textbooks indispensable for teachers and students. Therefore, their writing, production, printing and distribution need to be continuously examined and re-examined in the light of educational objectives (Gök, 2012). Stake and Easley (1978) noted that over 90% of all science teachers use a textbook 90 to 95% of the time (Eltinge, 1988). This close relationship between the textbook and the course is particularly true in biology topics.

In the opinion of Chiappetta, Sethna and Fillman (1991), science textbooks have a role in the development of a scientifically and technologically literate society. This particular role can be achieved by a content which stresses fairly equal proportions of knowledge, investigation, thinking, and the interaction between science, technology and society (Wilkinson, 1999). Hence, biology textbooks remain valuable and competent devices for learning about living world and related phenomena, offering organised, convenient sequences of ideas and information for teaching and learning (Gök, 2012).
According to Eltinge (1988), teacher’s questions, both for discussion and for testing, focus on information in the textbook. Students are trained to seek the “right” answers in textbooks. Other teaching aids, such as audio-visual materials supplement the textbook, and at times merely prove to be a means to present the same information as that in the textbook. Textbooks tend to focus on the disciplines of science. Science textbooks also place a great deal of emphasis on words and specialised terminology. In brief, what a student knows, does, or thinks regarding science in a classroom can be approached by reviewing two or three commonly used textbooks in a given discipline at a given level of instruction (Yager, 1983). Kabadere and Bal in Gök (2012) indicated that achievement in science education may also depend on the accuracy of content and quality of physical features of textbooks. This shows that textbooks are selective in what information is presented and how it is organised; yet they are also tied to the larger ideas with which students will be confronted outside the school/house walls (Fitzgerald, 2009).
Despite living in an era dominated by computer and smartphones, many science classrooms have limitations on using information and communication technology (ICT), which makes science textbooks still the most commonly used instructional materials. Results of a survey conducted by Yaman (1998), in which 254 teachers and 621 students around Turkey participated, indicated that textbooks are the main source of guidance for teachers and students during instruction, audio-visual instructional materials are rarely used in classrooms.
Furthermore, Koseoglu, Budak and Tumay in Gök (2012) noted that textbooks help teachers to decide the subject and the depth they should teach. This is true because textbooks are helpful for teachers who are inexperienced in their areas (Collette ; Chiappetta, 1984). In that regard, textbooks are helpful for the teacher in terms of providing homework, guiding practical, as keeping students busy if they finish the given task too soon (Wellington, 2000). They may function as a complement to the teacher’s lessons in teaching and learning. Teachers may use textbooks while they prepare their lesson plans, and activities found in textbooks may be used as extra materials (Gök, 2012).

According to Gök (2012), textbooks support teachers by aiding day-to-day planning and teaching, and long-term professional development. This is why Litz (2001) and Swanepoel (2010) opined that the main function of science textbooks is to support teachers and learners in the learning process. Thus, Mikk as cited in Swanepoel (2010) stated the following as the functions of textbooks in the support of students in their learning:
motivate students to learn
represent information (transform and systemise)
guide students to acquire knowledge
guide students to acquire learning strategies
aid self-assessment
differentiate
facilitate value education.
Features of Effective Science Textbooks
Although features that make a textbook effective differ between subject area and curriculum, textbooks in general must include some universal features. According to the National Research Council (1990), there are seven needs for biology textbooks in a scientific endeavour, which are:
Adequate but not encyclopaedic coverage
Factual accuracy
Incorporation of current conceptual understanding and new subject matter
Logical coherence
Clarity in explanation and effectiveness in illustrations
Appropriateness to students’ level and interest
Representation of biology as an experimental subject.

Likewise, according to the Florida University Department of Education (FLDOE, 2008), effective textbooks must include:
Instructional goals with adaptability to course requirements
Accurate, relevant, and relatively up-to-date information
Well-organised, coherent, and unified flow of information
Appropriate reading level and vocabulary
Effective layout, visual presentation, and physical features
Absence of stereotypes and biases
Multidisciplinary content with multiple rather than single perspectives
Small concepts taught as variations on larger themes
Development of insight and thinking skills rather than just memorisation of isolated or unrelated facts
Real-world applications of informational skills
Inclusion of supplemental and reference materials for teaching.
According to Blystone (1989), one very important thing that will make scientific terms and abstract knowledge to be more concrete and understandable is for the content of biology textbooks to be buoyed by appropriate and striking illustrations, real-life connections and different types of activities. Also, Ahtineva (as cited in Gök, 2012) asserted that tasks that had a link to real life motivated students.

There are so many textbooks that are in circulation in the Nigerian secondary schools. Textbooks as instructional material guide teachers in topic selection and provide ways to teach those topics. Jones, Kitetu and Sunderland (1997) asserted that textbooks serve the purpose of providing the learner with the opportunity to consolidate his/her understanding independently of the teacher. Many scholars like Gottfried and Kyle (1992) have also revealed that textbooks play a central role in the teaching of science and that the science curriculum is often designed around the structure of a textbook. The textbook for a biology course is the most consistently visible window on the biologist’s profession. Like the adorned prow of a sailing vessel, this general textbook characterises the ship known as biology (Blystone, Barnard, & Golimowski, 1990). The textbook is the most significant tool an instructor has in teaching biology and is a principal means by which the public learns of the progress, thoughts, and aspirations of the discipline called Biology (Blystone, 1987). They are important part of biology education and should encourage the students for investigating on diverse subjects using the questioning techniques, instruction approach, visual materials and activities (Çobanoglua, Sahin, & Karakaya, 2009). In summary, textbooks have an important place in biology education, therefore careful examination and comparison of the available textbooks should be undertaken before selection. In the long run, this should contribute to the development of more effective textbooks (Gök, 2012).

Various Analogies used in Presenting Genetics in Senior Secondary School Biology Textbooks
According to Harrison and Coll (2008), an analogy is a comparison of certain similarities between objects/ideas/events which are otherwise unlike will be adopted. An analogy consists of two components: the analogue and the target. The analogue; the familiar situation or object; provides a model through which students can make assumptions and inferences about the unfamiliar or new situation or object, called the target. For example, one analogy of the structure of an atom; the target; is the arrangement of planets orbiting the sun; the analogue. This definition and explanation of analogy is also supported by Duit (1991) and Harrison and Treagust (1994) who note that an analogy is an explanation that compares a fact that is unknown and unfamiliar with another known and familiar one. The unknown fact is the target while the known fact is the analogue. The analogy compares the similar characteristics of the target and analogue and then a transition from the known information area to the unknown information area is made.

An analogy is a mapping of knowledge between two domains such that the system of relationships that holds among the objects in the analogy domain also holds among the objects in the target domain (Gentner, 1989). This is why Mason and Sorzio (1996) were able to state that the purpose of an analogy is to transfer a system of relationships from a familiar domain to one that is less familiar. Glynn (2005) averred that: An analogy is a comparison of the similarities of two concepts. The familiar concept is called the analog and the unfamiliar one the target. Both the analog and the target have features (also called attributes). If the analog and the target share similar features, an analogy can be drawn between them. A systematic comparison, verbally or visually, between the features of the analog and target is called a mapping (Glynn, 2005).

Dikmenli (as cited in Dikmenli, 2015), showed that analogies in previous biology textbooks were generally used for biological concepts in relation to the structure and functions of the cell and nucleic acids. According to Orgill and Bodner (2004), effective analogies can clarify thinking, help students overcome misconceptions, and give students ways to visualize abstract concepts. Misleading or confusing analogies, on the other hand, can be more than just a waste of class time; they can interfere with students’ learning of class material (Orgill ; Bodner, 2004).

Analogy is mostly used for understanding abstract concepts and complicated issues. An analogy is an explanation that compares a fact that is unknown and unfamiliar with another known and familiar one. The unknown fact is the target while the known fact is the analogue. The analogy compares the similar characteristics of the target and analogue and then a transition from the known information area to the unknown information area is made (Duit, 1991). The analogue is known information while the target is a less known or unknown information. An analogy is an application of features in the analogue to the target concept. The more closely the analogue matches the target, the more effective and powerful the analogy is (Glynn, 1991).

When talking about effective teaching tools, analogies are the best practices to rely on as they help students convey new information to the available information structure, providing meaningful learning motivation and giving a new point of view on the subject (Glynn ; Takahashi, 1998). Analogies help to remove misconceptions and play an important role in conceptual exchange (Venville ; Treagust, 1996).

Analogies make abstract concepts concrete (Thiele ; Treagust, 1994). This teaching method makes complicated issues easier to understand with the help of analogy. While using analogy, it makes associations with real life, thus, it helps students visualise them by turning abstract concepts into more concrete ones. Analogies should therefore be chosen carefully and used in accordance with certain rules. Venville and Treagust (1996) assert that an analogy is a process of identifying similarities and differences between two objects or processes. Its purpose is to explain and name unknown cases via already known ones. According to Gentner (1998), it is called analogical mapping. Analogies serve as initial models to promote scientific concepts and are used frequently in science textbooks (Iding, 1997).

Venville and Treagust (as cited in Akçay, 2016) evaluated and classified the roles of analogies in the learning process into four main categories. The first category is the sense maker or advance organizer; it refers to analogies that provide an overview of a subject. The second category is the memory aid, which refers to analogies that contribute to retention of learning. The third category, transformer, refers to analogies with the ability to transfer knowledge from knowns (analogs) to unknowns (targets). The final category is that of the motivator, in which analogies raise students’ interest in a subject or course.
Where national science education literature is concerned, it is seen that more studies focus on analogies in biology textbooks (Dikmenli, 2010) than in science and technology (Dikmenli & K?ray, 2007 cited in Yener, 2012) and chemistry (?endur et al., 2011 cited in Yener, 2012) textbooks. For example, Dikmenli (2010), analysing the types of analogies used in high school biology textbooks in Turkey, scrutinised how these analogies are configured and presented. In this study, a total of 119 analogies were identified in seven biology textbooks. It was found that most of the analogies used in biology textbooks are configured and presented in the form of structural, verbal, concrete-abstract, embedded activator and simple analogies. In that study, it was revealed also that most of the analogies in the books are not configured according to the analogy-based teaching guides as analogies based on the teaching model are (Yener, 2012). Thiele, Venville and Treagust (1995) compared high school chemistry and biology textbooks for their use of analogies and found that analogies were used more in biology textbooks. Newton (2003) compared elementary school science textbooks with high school science textbooks in terms of their use of analogies.

Categories of Analogies
Curtis and Reigeluth (1984) categorised analogies and found an average of 8.3 analogies for each science textbook in the United States. Thiele and Treagust (1994) expanded Curtis and Reigeluth’s (1984) classifying system and categorised analogies in high school chemistry textbooks in Australia in a systematic way and found a total of 93 analogies in 10 books. Thus, the following are the categories of analogies used in textbooks as opined by to Curtis and Reigeluth (1984):
Analogical relationship: Structural (S), Functional (F), or Both (S;F). Three possible relational categories of analogical relationship can occur.

Presentational format: Verbal (V), Pictorial (P), or Pictorial-Verbal (P-V).

Content condition: Concrete to Concrete (C-C), Abstract to Abstract (A-A), or Concrete to Abstract (C-A). The actual content that is chosen to create the analog and target may be categorised in a variety of ways.
Position in text: Advance Organizer (AO), Embedded Activator (EA), or Post Synthesizer (PS).
Level of enrichment: Simple (S), Enriched (En), or Extended (Ex).

Then, there is the classification system of analogies as developed by Thiele and Treagust (1994). These are:
The analogical relationship between analogue and target
Structural: The analogue and target concepts in the analogy share attributes of shape, size, colour, etc.
Functional: The analogue and target concepts in the analogy share attributes of function, behaviour, etc.

Structural-Functional: The analogue and target concepts in the analogy share both structural and functional attributes.
The presentational format
Verbal: The analogy is presented in the text in a verbal format only.
Pictorial-Verbal: The analogy is presented in a verbal format along with a picture of the analogue.
The level of abstraction of the analogue and target concepts
Concrete-Concrete: Both the analogue and the target concepts are of a concrete nature.
Abstract-Abstract: Both the analogue and the target concepts are of an abstract nature.
Concrete-Abstract: The analogue concept is of a concrete nature but the target concept is abstract.
The position of the analogue relative to the target
Advance organizer: The analogue concept is presented before the target concept in the text.
Embedded activator: The analogue concept is presented with the target concept in the text.
Post synthesizer: The analogue concept is presented after the target concept in the text.
The level of enrichment
Simple: In this type of analogy, only one similarity is underlined between the analogue and target concepts. The analogy is formed of a simple sentence with no details.
Enriched: Two similarity dimensions between the analogue and target concepts are underlined. The analogical statement is formed of sentences which are basic for the analogy.
Extended: Two or more similarity dimensions between the analogue and target concepts are underlined. The analogical statement is formed of basic sentences including details. Analogies in which many sources have been used while explaining a target concept are also considered as extended analogies.

Pre-topic orientation
Analogue explanation: Introducing the analogue concept related to the target concept in the analogy through at least one point.
Strategy identification: Underlining that the text presented as an analogy is an assimilation.
Both analogue explanation and strategy identification: Underlining both the explanation of the analogue and the strategy identification.
None: Underlining neither the analogue explanation nor the strategy identification.

The limitations of the analogy: Underlining the situation that there are breaking points in analogies at which misunderstandings may possibly arise.

Importance of Analogies
The use of analogies in particular has been found to be very effective in prompting students to build understandings either through hands-on interactions with tangible resources (Richland ; Simms, 2015) or by making conceptual links with familiar objects, scenarios or events (Hagkund, Jeppsson, ; Andersson, 2012). Students either read the analogies in the textbooks or hear them through their teachers without filtering them (Dikmenli, 2015). The analogies in the textbook gain more importance due to the teaching strategies that are traditionally applied in teacher-centred classrooms (Dikmenli, 2015). Therefore, analysing the analogies that are used in presenting Genetics in senior secondary school Biology textbooks will contribute much to students, teachers, textbook authors, and programmers. Analogies are commonly used within the textbooks.
Scientific analogies have at least four distinguishable uses: discovery, development, evaluation, and exposition (Holyoak ; Thagard, 1995). Among them, the most exciting is discovery, in which the analogy contributes to the formation of a new hypothesis (Ugur, Dilber, Senpolat, ; Duzgun, 2012). Once a hypothesis has been formed, the analogy may facilitate further theoretical or experimental development. Analogy can also serve to form arguments for or against a hypothesis’ acceptance, and then the analogy can convey the new ideas to other people. For instance, Benjamin Franklin (Chiu & Lin, cited in Ugur et al. 2012) derived not only the idea for his experiment but also the basic hypothesis that lightning is electricity by grasping the lightning/electricity analogy. He also used that analogy to develop experiments. This implies that scientific analogies have been and can be used for more than one function for particular purposes.
In taking a cursory look at the function being played by analogies, Glynn, Britton, Semrud-Clikeman, and Muth (1989) opined that analogies serve an explanatory and creative function. Duit (1991) also agrees with this opinion that analogical reasoning can facilitate understanding and problem solving. Wong (1993) considered that generative analogies are dynamic tools that facilitate understanding, rather than representations of the correct and static explanations or solution. Other researchers (Harrison & Treagust, 1993; Brown, 1993) consider the use of analogies to be beneficial for conceptual change in science learning.
The use of analogies can result in better student engagement and interaction with a topic (Orgill & Bodner, 2004). Analogies allow new material, especially abstracts concepts, to be more easily assimilated with students’ prior knowledge, enabling them to develop a more scientific understanding of the concept (Ugur et al, 2012). Lemke (1990) asserts that students are three to four times more likely to pay attention to the familiar language of an analogy than to unfamiliar scientific language. The familiar language of an analogy can also give students who are unfamiliar or uncomfortable with scientific terms a way to express their understanding of and interact with a target concept.

Problems with Analogies Used in Biology Textbooks ; Classrooms
Despite the many advantages of the usage of analogies, there are perceived problems which are associated with the use in Biology (Genetics) textbooks and classrooms. Venville and Treagust (1997) described three of these problems, which are as follows:
Mechanical Clichés: In a comparison of biology and chemistry textbook analogies, Thiele et al. (1995) found that biology textbooks included many simple, non-elaborated analogies, for example: whip-like flagellum, mitochondria are the ‘powerhouse’ of the cell, ribosomes are protein factories’, the double helix structure of DNA is like a twisted ladder, and enzymes interact with substrates like a lock and key. The problem with these analogies is that they have become mechanical clichés that biologists, including teachers and textbook authors, use without thinking about the message being conveyed. Some of these analogies might be very useful to students if they were explained in a more detailed manner. For example, the lock and key model for enzyme interaction has the potential to help students understand the specific nature of enzymes. Without further explanation, how- ever, students are left to make their own conclusions about these biological concepts from the analogies. This leaves great potential for alternative conceptions to develop.
Student Unfamiliarity: If students are not familiar with the analog, then the likelihood that they will draw spurious conclusions about the science is greatly increased. In a local biology classroom, we observed a teacher explaining that red blood cells were shaped like a particular brand of candy that has an indent on each side of a disc. It turns out, however, that this brand of candy is no longer round but now has a square shape! Consequently, the use of this analogy may have resulted in this teacher’s students being confused about the shape of red blood cells. Thiele et al. (1995) also reported analogies such as the following in Australian high school biology textbooks. It is often helpful to think of a community, together with its non-living surroundings, as a system, just as one can speak of a political system or an economic system (Morgan, 1989). Few high school students would be sufficiently familiar with a political system or an economic system to draw relevant similarities with a biological system. This problem arises because it is often the teacher or textbook author who generates the analogy and, subsequently, they neglect to ensure student understanding of the analogy.

Inconsistencies between Analogy and Target: It is the nature of analogies that the analogy and target are not exactly the same. Students may be led to believe that the two concepts share features which in fact they do not. For this reason, it seems important that teachers explicitly map the shared attributes and delineate the limitations of analogies. It also may be advantageous if students are given some kind of training on how to use analogies when learning science (Venville, Bryer, ; Treagust, 1994).

According to Duit (1991), there are some disadvantages when analogies are not used well. This is because it is not all analogies are good analogies, and neither are all good analogies useful for all students (Orgill ; Bodner, 2004). In an analogy, if the analogue and target concepts do not fully overlap with each other, they can lead students to form erroneous concepts and make mistakes (Clement, 1993). Analogies in textbooks are usually used randomly and are inadequate for students (Gilbert, 1989), which causes them to make mistakes (Thiele ; Treagust, 1994).

Analogies are double-edged swords: They can foster understanding, and can also lead to misconceptions (Glynn, 2008). As Duit, Roth, Komorek, and Wilbers (2001) explain:
A growing body of research shows that analogies may be powerful tools for guiding students from their pre-instructional conceptions towards science concepts. But it has also become apparent that analogies may deeply mislead students’ learning processes. Conceptual change, to put it into other words, may be both supported and hampered by the same analogy.

Nonetheless, the effective analogy use fosters understanding and avoids misconceptions (Duit & Glynn, 1995).

More so, despite their advantages and usefulness, analogies can cause incorrect or impaired learning, depending on the analog-target relationship (Ugur et al, 2012). For example, if the analog is unfamiliar to the learner, development of systematic understanding is precluded. Although analogies may be more useful to students who primarily function at the concrete operational level (Gabel & Sherwood, 1980), if students lack visual imagery analogical reasoning may be limited. Students already functioning at a formal operational level may have an adequate understanding of the target and the inclusion of an analogy might add unnecessary information or noise (Johnstone & Al-Naeme, 1991). For these reasons, some teachers choose not to use analogies at all and thereby avoid these problems while, at the same time, forsaking the advantages of analogy use (Ugur et al, 2012).

Also, the mechanical use of an analogy may be due to students’ inability to differentiate the analogy from reality. An analogy never completely describes a target concept (Orgill ; Bodner, 2004). Each analogy has limitations. Unfortunately, students usually do not know enough about the target concept to understand those limitations. For this reason, they may either accept the analogical explanation as a statement of reality about the target concept or incorrectly apply the analogy by taking it too far (Orgill ; Bodner, 2004).

There are also potential problems associated with the use of analogies in textbooks. The text analogies are very different from oral analogies because they offer no mechanism for immediate feedback or modi?cation for individual students or for the correction of misconceptions that students might develop from the printed analogies (Orgill ; Bodner, 2006). This is because text analogies are not often presented in such a way that their explanations are very clear in order to be effective. It is indeed a very big problem when it comes to the use of analogies.
Another problem which exist in analogies used in biology textbooks is the fact that textbook analogies are not often explained clearly (Orgill ; Bodner, 2006). Duit (1991) was able to note that over half of the analogies in textbooks are not explained at all, and few analogies are explained completely. Thiele and Treagust (1995) are even of the opinion that comments from textbook authors indicate that they believe that either the students themselves should be capable of explaining the analogy or that the teachers should explain each analogy in the textbook they use to their students. For similar reasons, textbook authors rarely state the limitations of any analogy they present in their textbooks (Thiele ; Treagust, 1995).

How Should Teachers Use Analogies in Biology?
It appears from the discussion above that analogies are certainly a prickly issue in biology education, especially in the presentation of genetics. They may well be able to improve student understanding of some biological concepts; however, it is clear that using analogies can also create problems. Teachers have often stated that the analogies they use are suitable and have encouraged other teachers to use similar procedures (See Biermann 1988; Stencel ; Barkoff 1993). But, how can teachers take advantage of these and other analogies as a pedagogical tool while keeping the misdirection and miscomprehension that may result from their use to a minimum?
Different models for the use of analogies in science education have been developed (See Gentner ; Gentner 1983; Zeitoun 1984; Glynn 1991). Of these, the one which is often used mostly is the Glynn’s Teaching with Analogies Model (TWA). The TWA model explains the rules that teachers need to follow during analogy-based teaching. These rules comprise the following six steps (Glynn, 1991):
Introduce the target concept;
Cue retrieval of the analogue concept;
Identify relevant features of the target and analogue;
Map similarities;
Indicate where the analogy breaks down; and
Draw conclusions
FOCUS
CONCEPT Is it difficult, unfamiliar or abstract?
STUDENTS What ideas do the students already have about the concept?
ANALOG Is it something your students are familiar with?
ACTION
LIKES Discuss the features of the analog and the science concept.
Draw similarities between them.

UNLIKES Discuss where the analog is unlike the science concept.

REFLECTION
CONCLUSION Was the analogy clear and useful, or confusing?
IMPROVEMENTS Refocus as above in light of outcomes
FOCUS
CONCEPT Is it difficult, unfamiliar or abstract?
STUDENTS What ideas do the students already have about the concept?
ANALOG Is it something your students are familiar with?
ACTION
LIKES Discuss the features of the analog and the science concept.
Draw similarities between them.

UNLIKES Discuss where the analog is unlike the science concept.

REFLECTION
CONCLUSION Was the analogy clear and useful, or confusing?
IMPROVEMENTS Refocus as above in light of outcomes

Figure SEQ Figure * ARABIC 2: The FAR Guide for teaching and learning science with analogies (Treagust et al. 1994)
This model was developed from the examination of exemplary textbook analogies, and key operations performed by the authors were incorporated into a six-step model which was designed as a guide for teachers and authors of science textbooks (Venville & Treagust, 1997). Venville and Treagust (1997) have modified the model that was developed by Glynn and have provided in service education for teachers using the Teaching-With-Analogies Model. However, the exemplary teachers working on a series of collaborative exercises adapted and modified this model to suit the classroom situation. Analysis of their teaching resulted in the development of a three-phase model which appears to be more efficient and effective (Venville & Treagust, 1997). The three phases of the model, which are: Focus, Action and Reflection, are used to form the acronym FAR. ‘The FAR Guide for teaching and learning science with analogies’ (Treagust et al. 1994). Because of the inductive manner in which the FAR Guide has evolved from exemplary science teachers’ practice, this model probably has the greatest potential for improving science teachers’ use of analogies (Venville & Treagust, 1997.
The FAR Guide (see Figure 2) was developed within a constructivist theoretical framework with particular emphasis on the use of analogies to engender conceptual change. It aims to maximise the benefits and minimise the constraints of analogies when used to teach science. The guidelines are practical and clearly address the problems associated with analogies which have been described above. These three phases are discussed below (Venville & Treagust, 1997):
The first phase of the FAR Guide is Focus. Teachers are encouraged to focus on the science content to ascertain why it is difficult, focus on the analog to ensure it is familiar to the students, and focus on the students themselves to consider the ideas they already have about the science concept.
The second phase of the FAR Guide is Action. Here it is considered imperative that the teacher and students discuss both the similarities and differences between the science concept and the analog so that the limitations of the analogy are clearly delineated.
The final phase of the FAR Guide is to reflect on the analogy, to draw conclusions and decide whether it was clear and useful or confusing, and to improve the analogy in light of this reflection. Used in an optimal manner, analogies can be a useful strategy for developing common knowledge and shared meaning between teacher and student. If science teachers were able to follow the steps of the FAR Guide, then the result would be a cyclic process of improvement and modification of the analogies they use (Venville & Treagust, 1997).
The most important potential benefit would be that science teachers would consider each analogy and its possible pitfalls before they used them. Feedback from science teachers who have participated in workshops using the FAR Guide indicate that the approach has enabled teachers to improve their analogical instruction as part of their teaching repertoire (Treagust, Venville & Harrison 1994).
As stated by Glynn (2008), one implication of the Teaching-With-Analogies Model is that teachers should try to select analogs that share many similar features with the target concept. In general, the more features shared, the better the analogy. Another implication is that teachers should verify that students have not formed misconceptions. One way to do this is to ask focused questions about features that are not shared between the analog and the target concept (Glynn, 2008).

Empirical Studies
Previous Studies on Genetics
Haambokoma (2007) article reported a study conducted to determine the nature and causes of learning difficulties students encounter in genetics at high school level in Zambia. A survey design was used and data were obtained from students and teachers using interview schedules and self-completion questionnaires. Quota sampling procedure was used to select the sample from the target population. Data collected were analysed using content analysis approach. The study found that students had difficulties understanding among others genetic crosses genetic terms, mitosis and meiosis as well as mutation. Factors identified to have caused learning difficulties included: inability by teachers to explain clearly to students; none teaching of the topic; topic taught near examination time, fast presentation of lessons by some teachers; belief by some students that genetics was difficult to learn; lack of appropriate learning aids and inadequate time allocated to teaching of the topic. Some of the recommendations made were that: teacher training institutions must prepare biology teachers adequately to teach this topic well; adequate time should be allocated to teaching of genetics; teachers need in-service training to enable them use appropriate teaching methods for teaching genetics.

Agogo and Naakaa (2014) investigated how the 5Es constructivist instructional strategy would improve students’ interest in senior secondary school genetics in Gwer Local Government Area of Benue State, Nigeria. The design of the study was Quasi: experimental, specifically, the pretest post-test non-equivalent control group design. A sample of 147 students from four schools, out of a population of 2,183 SSII biology students. A validated 30 item Genetics Interest Inventory (GII) was the instrument for data collection. A reliability co-efficient of 0.85 was established for the GII using Cronbach Alpha method. Out of the four schools, two schools were assigned to the experimental group while the other two to the control group. The experimental group were taught genetics using the 5Es (engagement, exploration explanation elaboration and evaluation) constructivist instructional strategy while the control group were taught using the conventional (lecture) method. Mean and standard deviation were used to answer the two research questions and Analysis of Covariance. (ANCOVA) was used to test the two hypotheses at P;0.05 level of significance. The result revealed that the 5Es constructivist instructional strategy was more effective in facilitating students’ interest in genetics in both urban and rural schools. The study recommended among others, that the 5Es constructivist instructional strategy be adopted in our school system for teaching biology, especially genetics.

In another study, Clément and Castéra (2013) discussed that the presentation of human genetics is now less deterministic, formulated in a more systemic approach, taking into account the interaction between the genes and their environment (epigenetics), discussing the notion of biological determinism, and including connections with ethical and social implications. How are these new genetic trends represented today in biology textbooks? Do multiple ways exist across cultures, languages, and countries? Two complementary sets of data are presented and discussed: (1) the representation of human genetic diseases in French biology textbooks, showing a frequent absence of a systemic approach with nevertheless some exceptions; and (2) a comparative analysis of biology textbooks in 16 countries, showing the common similarity in their use of an implicit message through the same clothes and hairstyle of identical twins, but strong differences—in their use of the metaphor genetic programme—which depended on the sociocultural context of each country. We argue that the renewal of the taught representations of human genetics is not only correlated with the renewal of scientific knowledge, but also with implicit values underlying each country’s sociocultural context.

The purpose of the research of Venville and Donovan (2008) was to explore the way pupils of different age groups use a model to understand abstract concepts in genetics. Pupils from early childhood to late adolescence were taught about genes and DNA using an analogical model (the wool model) during their regular biology classes. Changing conceptual understandings of the concepts of gene and DNA as a result of the teaching that incorporated the model were investigated. The research design was a multiple case study enacted in four classes (Year 2, Year 5, Year 9 and Year 12). In each class, the teacher used the same wool model to engage pupils in learning about genes and DNA. The results suggest that the role of the wool model was largely determined by the pupils’ prior knowledge. The model was malleable and had multiple roles in the teaching and learning process that reflected the pupils’ developing conceptual understandings about genes and DNA.

Ekong et al (2015) conducted a comparative ex-post facto study to investigate factors that could influence the performance of students in Genetics. The sample for the study was drawn from 200 Level students in the Departments of Biochemistry, Biological Sciences and Microbiology, Federal University Wukari, Taraba State, Nigeria. Simple random sampling was used to select 100 students from the 150 in the class. A 12-item structured questionnaire was used to obtain data on students’ attitude towards Genetics, mode of admission, gender and school type while the instrument titled ‘Genetics Concepts Achievement Test’ (GCAT), which comprised 40 multiple option questions, was used to measure the students’ performance in genetics. The first null hypothesis was tested using percentages while the remaining hypotheses were tested with Independent Sample T-test. The data collected was subjected to descriptive statistics using the SPSS version 17.0 software and the results were coded and tabulated. Findings from results indicate that students had a generally positive attitude towards Genetics. The t-test analysis revealed a significant difference (P=0.05) for type of school attended and a non-significant difference for students’ gender and mode of entry into the university. This study is of great significance to teachers and policy makers since the current trend is towards the improvement of students’ academic performances in STEM courses so as to fast-track national development. To bridge the gap between the day and boarding schools, these researchers recommend the provision of adequate teaching resources for all schools as these play vital roles in the enhancement of students’ academic performance.

According to Aivelo and Uitto (2015), genetics is a fast-developing field and it has been argued that genetics education is lagging behind. Genetics education has, for example, been suspected of indoctrinating strong genetic determinism. As the updating of the national upper secondary school curricula is about to start, we decided to study how the current curriculum manifests in Finnish biology textbooks. We studied the main four textbooks for historical gene models and definitions of genes using content analysis. Hybrid models were pervasive in textbooks. The textbooks expressed sometimes even strong genetic determinism, which might be linked to the dominance of older historical models in the textbooks. We also found instances of determinism which we call ‘weak determinism’: genes were depicted as more important factor than environment in relation to the expressed properties. Subsequently, there were no modern gene models found. We suggest gene models should be presented explicitly to reduce misconceptions about genes. We argue that genetics education needs to take more into account than environmental effects and there needs to be more emphasis on the temporal and developmental aspect of genotype-phenotype link. Specifically, in Finland, this could be done by a more explicit formulation of the national curriculum.

Previous Studies on Analogies
In this paper by Guerra-Ramos (2011), there is a critical overview of the role of analogies as tools for meaning making in science education, their advantages and disadvantages. Two empirical studies on the use of analogies in primary classrooms are discussed and analysed. In the first study, the ‘string circuit’ analogy was used in the teaching of electric circuits with students aged 8-9. In the second study, the ‘making a cake’ analogy was introduced within the study of photosynthesis with students aged 10-11. Outcomes of both studies are scrutinised to assess the effectiveness of analogies as tools for meaning making. How the analogies are presented, their contexts, and how much students are involved in mapping the analogical relations appear to be determinant. This strongly suggests that research and pedagogical practice should shift from determining the effectiveness of analogy in cognitive transfer, from analogue to target domains, towards the recognition of its role in generating engagement in developing meaningful explanations through discourse. Finally, most salient aspects of the use of analogies are considered for contexts in which they are used to promote understanding of scientific ideas. Analogy can play and important role in that task if it is seen as a resource to promote understanding and meaning making but its strengths and limitations are not ignored.

Yener (2012), carried out a research to determine how analogies are structured in physics textbooks. The aim of this study was to scrutinise the types of analogies used in physics textbooks in High Schools, and to study how these analogies are structured and presented. In this study, four physics textbooks were examined using the descriptive analysis method. Analogies detected in textbooks are classified according to criteria such as the Analogical Relationship, Presentational Format, Condition of Subject Matter, Position in Text, Level of Enrichment, Pre-Topic Orientation and Limitations. As a result of the analysis, a total of 50 analogies were detected in four physics textbooks. It was determined that these were mostly configured as functional, verbal, concrete-abstract, embedded activator, and simple analogies. The results are compared with science teaching literature and recommendations are developed.

The study of Maharaj-Sharma and Sharma (2015) was undertaken to examine and interpret how science teachers in Trinidad and Tobago used analogies in their science teaching. A total of 30 lessons taught by five different teachers were observed and analysed using an interpretative research methodology to develop generalized observations. The findings revealed that in general science teachers used few analogies in their teaching and that the analogies used ranged from simple to technical. Interviews following the classroom observations revealed that the teachers were knowledgeable about analogy use in science teaching and about some of the benefits and challenges of using analogies to teach science. The research suggests that effective use of analogies in classroom science teaching is an area that needs attention from two perspectives: 1) development or acquisition of relevant analogies for use by teachers and 2) reorientation of teachers through professional training into a view of learners as constructors of knowledge instead of passive knowledge receptors.

A collection of analogies is presented by Woody and Himelblau (2013) that are intended to help students better understand the foreign and often nuanced vocabulary of the genetics curriculum. Why is it called the wild type? What is the difference between a locus, a gene, and an allele? What is the functional (versus a rule-based) distinction between dominant and recessive alleles? It is our hope that by using these analogies teachers at all levels of the K-16 curriculum can appeal to the common experience and common sense of their students to lay a solid foundation for mastery of genetics and, thereby, to enhance understanding of evolutionary principles.

In the article of Orgill and Bodner (2004), analogies can be powerful teaching tools because they can make new material intelligible to students by comparing it to material that is already familiar. It is clear, though, that not all analogies are good and that not all “good” analogies are useful to all students. In order to determine which analogies are useful for students and how analogies should be presented to be useful for students, we interviewed biochemistry students about the analogies that were used in their classes. The authors found that most biochemistry students like, pay particular attention to, and remember the analogies their instructors provide. They use these analogies to understand, visualize, and recall information from class. They argue, however, that analogies are not presented as effectively as they could be in class. We present their suggestions for improving classroom analogy use.

In another study, Orgill and Bodner (2006) reported the results of an analysis of the use of analogies in eight biochemistry textbooks, which included textbooks written for one-semester survey biochemistry courses for non-majors; two-semester courses for chemistry or biochemistry majors; and biochemistry courses for medical school students. They presented an analysis of how analogies are used and presented in biochemistry textbooks, and compared the use of analogies in biochemistry textbooks to the use of analogies in other science textbooks. They also compared the use of analogies in biochemistry textbooks with the factors known to promote spontaneous transfer of attributes and relations from analog concept to target concept.

Venville and Treagust (1996) conducted a case study employing student and teacher interviews after analogy-related lessons. Nine different teachers were used in their three-year study. The researchers concluded that teachers used analogies in four different roles, as a sense-maker, a memory-aid, a transformer, and a motivator. The teaching style of the teacher and the teacher’s intention played a major role in choosing a specific analogy.

Ugur et al (2012) investigated the effects of analogy on the elimination of students’ misconceptions about direct current circuits, students’ achievement and the attitudes towards physics lessons. The sample of this study consisted of 51 11th grade students from two different classes. While one of the classes was the experimental group where analogy was used in the lessons, the other class was the control group where the traditional methods are employed in lessons and this selection was made randomly. When the obtained results were examined, it was seen that teaching with analogy has a significantly positive effect on the elimination of misconception and achievement although it has almost no effect on the attitudes of towards physics.

Dagher (1995) conducted an analysis of analogies used by classroom teachers. Forty transcripts from 20 seventh and eighth grade science teachers ranging in experience from 1 to 20 years were reviewed. The teachers knew that they were being observed for teacher-student interactions, but nothing was stated about analogy use. It was found that just over half of those teachers used verbal analogies in their teaching. The analogies were used mainly in an explanatory or descriptive nature. There was a wide variety in the extent to which the analogies were developed. Most of the analogies appealed to common student understanding. What was not analysed in this study, however, was the effectiveness those analogies had on student comprehension.
Appraisal of Literature
From the reviewed literatures, the concept of genetics has been seen as a very difficult topic that has affected many students negatively in their senior secondary school examination. The results of these examinations for over a period of time have really shown that genetics is a topic which students have constantly failed to answer properly. Nevertheless, the concept of analogies from the literature reviewed have shown to be effective in helping students out in looking for solution to the difficult topic, howbeit with its own challenges. This study thus focuses on the assessment of analogies used in presenting genetics in senior secondary school biology textbooks in Osun State.

CHAPTER THREE
METHODOLOGY
This chapter describes the method used in carrying out the study. It examines the research design, population, sample and sampling technique, the instruments used for data collection and data collection procedure as well as validation of the instruments and the method of analysis of the collected data.

Research DesignThe study will adopt descriptive survey research design. This is because the research seeks to study a population from which a sample will be drawn. The method will be adopted for the purpose of gathering information for describing and analysing information on analogies used in the presentation of genetics in senior secondary school biology textbooks in Osun State. The survey research design will allow the researcher to obtain accurate data from the population used for the study.
Population, Sample, and Sampling TechniqueThe population for this study will comprise all recommended Biology textbooks used to implement biology in Osun state senior secondary school. The sample will comprise six (6) out of the nine (9) recommended biology textbooks in Osun state using simple random sampling technique.
Research InstrumentsThe data collection instrument to be used in this study is Biology Textbooks Genetics Analogy (BTGA). This will be used to obtain information on the presentational format (Verbal, pictorial or pictorial-synthesizer), and the level of enrichment of the analogies (simple, enriched or extended).

Validation and Reliability of Instrument
The research instrument will be validated by the professional help of the supervisor and two (2) other experts in the Department of Science and Technology Education, Faculty of Education, Obafemi Awolowo University, Ile-Ife for both face and content validity. The experts will read through the contents and make necessary corrections. Reliability of the instrument would be gotten using appropriate reliability tests.

Method of Data Collection
The researcher will employ survey method and content analysis technique of identifying analogies in the selected Biology textbooks. The researcher will read through the selected Biology textbooks thoroughly, identify the analogies, compare the use of the analogies and describe the analogies.
Analysis of Data
Data collected will be analysed using frequent count and percentage. A bar chart will be drawn illustrating the percentage distribution of the analogies in the selected six (6) Biology textbooks.
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