Searching for clarity to teach the complexity
of the gene concept
by G. Venville and J.
Donovan
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The paper was originally published in Teaching Science, vol. 51, 3:20-24, Spring 2005 issue, published by the Australian Science Teachers Association, asta@asta.edu.au Grady Venville is an Associate Professor in Science and Technology Education at Edith Cowan University. She is a passionate advocate of strong links between school science, science teacher education and research in science education. Jenny Donovan holds a research position in science education at Edith Cowan University that is supported by many years of teaching high school biology and human biology, many different university science units, and her own choir. |
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The discrete concept of the gene belongs to a bygone era of science. This article explores the contemporary science literature and nine 'expert geneticists' views about today's bewildering gene concept. This information is used to make clear suggestions about how biology teachers should teach the complexity of the gene concept. |
It has been argued that the concept of the gene that is used by both the general public and by many scientists is completely outmoded (Morange, 2001). This argument is not surprising when we consider that the gene concept was constructed well before the discovery of the structure of DNA in 1953. Our understanding of molecular genetics has increased exponentially since that time. Morange maintains, however, that, 'even if it is impossible to give a general definition of the gene, the concept of the gene, even if it is vague, is indispensable for modern biology' (p. 5). If the concept of the gene is vague, impossible to define, but indispensable, as Morange suggests, what does this mean for high school genetics? How should we be teaching the concept of the gene so that students are adequately prepared for the decision making that will be required of them as they live in the age of biotechnology? The purpose of this paper is to begin to explore answers to these questions. In order to provide a context for the discussion we draw on information from two sources. The first source of information is contemporary science literature about the concept of the gene and the notion of the gene as an evolving concept. The second source of information is expert geneticists' views of the gene and their views about teaching this concept that we have ascertained through interviews. We then contemplate how this concept can be represented in the high school science class of the future.
2. The evolving concept of the gene
! The concept of the gene is and always has been a continuously evolving one (Portin, 1993). Falk (1986) outlines four concepts of the gene that he believes had the most importance in the past century (Fig. 1). These include the instrumental gene, the material gene, the DNA gene and the bewildering gene. Falk's instrumental gene is something that he believed the researchers of the earlier part of the twentieth century understood as discrete units that obeyed the basic Mendelian laws and were allocated the potentiality for a single trait.
The second concept of the gene that Falk (1986) discusses is the material gene that coincided with the realisation that genes are located on chromosomes and therefore are material entities. The discovery of DNA's double helix, attributed to Watson, Crick and Wilkins, though based on Rosalind Franklin's X-ray diffraction work, was the turning point from the material gene concept to what Falk (1986) called the DNA gene concept (Fig. 1). Fox-Keller (2000) claims that Jacob and Monod's work on gene regulation must be considered one of the triumphs of early molecular genetics. The notion that the same genes in different cells could be activated at different times challenged the idea that genes are autonomous, causal agents. When research expanded to the study of eucaryotes, rather than procaryotes, many other assumptions about genes that came with the DNA gene concept began to be questioned. Falk (1986) describes Britton and Kohne's discovery in 1968, that much of the DNA in eucaryotes is highly repetitive and redundant, as the turning point to the new notion of the bewildering gene (Fig. 1).
Fig. 1. A schematic representation of Falk's (1986) description of concepts of the gene in the past century.
3. Today's difficult to define gene
The concept of the bewildering gene as described by Falk (1986) coincides with many other discoveries that also contradicted the concept of the discrete, material, gene. For example, the discovery that segments of DNA may code for two different polypeptides defies the earlier ideas of genes coding for a single enzyme or a different kind of protein. Another example Falk (1986) discusses is the discovery of unstable or 'jumping genes' by Barbara McClintock in the 1940s. It has only been possible for McClintock's notion of the genome as a 'dynamic organ' to be accepted in more recent times with a bewildering array of examples of what a gene can be (Fox-Keller, 1983). Discoveries such as repeated genes, split genes and alternative splicing, assembled genes, overlapping genes, transposable genes, polyprotein genes and nested genes have left us with a 'rather abstract, open, and generalized concept of the gene, even though our comprehension of the structure and organization of the genetic material has greatly increased' (Portin, 1993, p. 173).
The change in conceptual understanding that Fox-Keller (2000) sees as being important over the past century is the notion of genetic stability. Today, Fox-Keller explains, the balance between genetic stability and mutability is seen to shift in response to the particular environment in which the cell finds itself. This is a far cry from the traditional view of DNA as an inherently stable molecule subject to occasional random errors. Tudge (2000) supports this modem, 'anarchic' (p. 141) view of the gene by explaining that the DNA is far more restless than is often supposed, with individual bits of DNA doing their own thing by detaching from allotted places in a chromosome and then inserting somewhere else in a random fashion.
4. Is the gene concept outmoded?
Morange (2001) argues that the concept of the gene is useful for understanding both the genetic basis for a large number of illnesses and for describing development. The main thrust of his argument, however, is that the current, popular concept of the gene is outmoded because people believe, in a literal sense, that genes determine or cause behaviours and characteristics. The popular concept of the gene is reflected in the everyday way people talk about genes. For example, it is common for people to say things like, '1 got the gene for big feet from my father,' or 'Hot temper runs in my family, we all got that mean gene!' The popular concept of the gene also is reflected in myths such as the ' designer baby' that give the impression that soon parents will be able to select for their babies 'genes' for certain eye colour, body shape and intelligence. This popular image of the gene was observed in a number of studies that established student understandings in genetics (Lewis & Kattmann, 2004; Venville & Treagust, 1998). The study in high school of Mendel's experiments on pea plants potentially gives some kind of scientific verification to this simplistic, popular concept in the minds of students.
In his book, The Misunderstood Gene, Morange investigates the genetic basis of a number of human behaviours and characteristics such as learning, memory, cancer, development, aging, intelligence and altruism. His message is that while genes are necessary for the realization of all complex behaviours, they are not specific to any of these processes. He explains that in most biological situations, natural selection has molded gene function without creating a direct link between a gene and the selected characteristic. In this sense, the 'youth gene', for example, is, and always will be, a myth.
It is important that people understand that genes rarely determine the gross characteristics of an organism such as nose shape or leaf texture, but they contribute to them, they are involved in their realization. Morange (2001) and Nelkin and Lindee (2004) warn that the gene concept has evolved into something onto which the people of today are apt to project their fears and fantasies. For example, while many people would have a fantasy that their child has inherited a 'gene for intelligence or learning' or fear that their child may not have inherited such a gene, Morange explains that genes involved in learning are not specific to this process. They code for ordinary proteins that are involved in intercellular interactions and intracellular signalling pathways. There are no proteins specific to learning and memory but rather a bevy of proteins that, through their function as relays or transmitters, have been harnessed by evolution in the development of cognitive processes.
In a similar way to Morange (2001), Fox-Keller (2000) agrees that the image of genes as distinct entities that cause organisms to look, develop and behave in particular ways is outmoded. Fox-Keller argues throughout her book that our new understandings of the complexity of genes and their expression within and between the levels of cell, tissue, organ and system, has critically undermined the conceptual adequacy of single genes as direct causes of phenotype. She explains that single gene disorders such as Tay-Sachs, Huntington's disease, cystic fibrosis, thalassemia, and phenylketonuria are rare examples of diseases that are caused by a single genetic allele and that diseases that are influenced by many genes are more the norm. Unfortunately, because Mendel is still the starting point for many genetics curricula, these diseases are discussed in textbooks as they are human examples that fit most closely with Mendelian genes. By their selection, they lock students into the Mendelian view of the gene.
5. Consulting experts about their concept of the gene
In order to further explore issues about the concept of the gene that may be relevant to school science, we interviewed nine ' experts' in genetics. These people included a range of geneticists from population geneticists to molecular geneticists, and included genetics counsellors and educators. All the experts had some experience with education, such as public, tertiary or secondary level education. A profile of the nine geneticists genetics expertise, educational experience and specific interests is presented in Figure 2. The experts were presented with the current WA Human Biology high school curriculum (which is still very Mendelian) and then asked to respond to it in terms of their own thinking (metaphors, mental pictures) about genes. Other questions included how outmoded they considered the Mendelian view of a gene to be, and what did they see as key concept with which students should emerge from school, plus effective ways in which these concepts could be developed.
Transcripts of the interviews were analysed independently by both authors of this paper. Themes that emerged from the data about the experts' vision of a gene were highlighted and compared. Collaboratively the authors agreed that there were four important themes that clearly emerged from the data. The first major theme that emerged from the interviews with experts was that genes are regions of DNA that are a code for making polypeptides. The second theme was that genetic determinism is a myth and the third theme was related to the importance of the impact of the environment on the phenotype of living things. The fourth theme was about genetic control and
gene expression. Subsequent to the themes being clarified, the authors completed a search for disconfirming evidence and highlighted aspects of the interviews that contradicted, or were tangential, to the established themes. Each of the major themes, as well as the disconfirming evidence, is explored in the following paragraphs.
Fig. 2. A profile of the geneticists' genetics expertise, educational experience and areas of interest.
6. Experts' vision of the gene
Theme 1: Genes code for polypeptide production
Every expert, at some point in the interview, made an explicit connection between genes, DNA, polypeptides and proteins while discussing their concept of a gene. While they used different terminology, the notion that genes are regions of DNA that code for the production of polypeptides that form proteins was clearly evident in the way that each of the experts either expressed their own understanding of a gene or explained what they felt high school students should understand about the gene. Excerpts from interviews that demonstrate the experts' ideas follow.
Expert 1: [I think of the gene] in terms of being a coding sequence for parts of proteins. It contains structural components responsible for its existence within a chromosome.Expert 5: There's a schematic picture 1 have in my mind, where I draw exons, introns into a gene map. I think of it from the sequencing data, of all the bases... It's important to know that they encode for mRNA, which is then translated into proteins.
Expert 9: The operon theory tells us the bits of DNA that make up a gene are not like a string of pearls on a strand, they are scattered.
Expert 3: For myself, I think of a gene as a transcribed region of DNA, quite a scientific perspective, primarily a structural way of thinking. I also think of it as. a set of instructions. In other words, I use both a literal and a more metaphorical way of thinking.
There was evidence that some of the experts use different views of a gene depending on the audience or the purpose of their work.
Expert 7: I am a population geneticist, but my view of a gene really varies with the audience to whom I am talking... We have come so far in genetics, proteomics, and seeing cellular changes. [When I talk to the general community] I try to talk about things they can see where possible, such as chromosomes, which I refer to as beads on a chain or string... I talk about genes on chromosomes that affect your risk of getting cystic fibrosis or haem achromatosis or whatever... When I talk to health professionals I hardly mention genes and talk about alleles or point mutations instead.Expert 3: How I think about it myself in a lab is probably different from how I might explain it to a student. I think of a gene as a transcribed region of DNA....
Tudge (2000) explains that biologists still think of genes in abstract terms when it suits them to do so, but they can also think of them as chemical entities, involved in complicated chemistry. He says that breeders, physicians, conservation biologists and others often think of genes as beads on strings, as our Expert 3 explained, but that this classical vision of the gene is now often crossreferenced with molecular biology in a powerful combination.
Theme 2: Genetic determinism is a myth
The majority of the experts were very expressive about the complexity of the structure and function of the gene and the notion that a single gene determines a single characteristic rarely is a true reflection of their vision of genetic reality. They were often emphatic about debunking the common belief that a gene determines a particular characteristic. This was expressed through their understandings of several factors such as variable I expressivity, polygenic characteristics (characteristics influenced by more than one gene) and pleiotropy (genes that affect more than one characteristic).
Expert 8: I have never thought of a gene that determines a morphological feature and that's it. I had the benefit of a rigorous genetics education, so the concept of pleiotropy, one gene affecting many characters, has always been part of my understanding and part of my teaching... Rolling tongue, ear lobes etc are all myths in terms of being inherited through single genes. In reality they are probably I polygenic characters.Expert 6: But to me the biggest message has to be that most i of our traits are polygenic and multifactorial and you must never forget the influence of the environment.
Expert 5: One of the things that I think would be important to teach in this is not only to understand how genes interact and how they work, but also how genes express themselves and how they do work in concert with one another. There are a lot of so-called monogenetic stories where one gene determines your entire outcome and the entire way you work. If I were teaching some of this, I would think it important to give a discreet amount of time to gene-gene and geneenvironment interactions and nondeterminism. Yes, of course, if you have a catastrophic gene alteration that leads you to have something like Duchenne Muscular Dystrophy, then of course, that is deterministic, but the vast majority of gene alterations, and the ways genes work, is notin a monogenetic fashion ... People aren't relating [genetics] to a hierarchy of complexity-DNA, gene, chromosome, nucleus, cell, tissue, organ, system, person. It' s no wonder students have difficulty tying it all together.
One expert, while aware, like the other experts, of the inaccuracy of the idea that one gene codes for one protein, paradoxically stated that this may still have its use in terms of schooling.
Expert 3: The idea of one gene [coding for] one protein, although it's incorrect, it's probably the best starting point at that [school] level.
One population geneticist, in contrast with the other experts, said he has a pre-DNA vision of a gene; that a gene is, in essence, a code for a single character. However, he augmented this vision by saying that he has a hybrid model for the gene because he also understands biosynthesis, or the production of I organic molecules.
Expert 9: As a population geneticist, my metaphor is that a gene is the material code for one elementary character of an organism. That is a pre-DNA definition... I have a hybrid understanding of a gene ... To understand the molecular mechanism of the determination of characters you have to understand biosynthesis.
Tudge (2000), like Expert 3, argues that while most phenotypic characteristics are polygenic, and that most genes are pleiotropic, 'the central observation "one gene, one protein" is the simple case that encapsulates the essence. All other cases (albeit the majority) are, elaborations' (p. 119).
Theme 3: The environment impacts on phenotype
Six of the nine experts explicitly mentioned the environment in determining phenotype.
Expert 8: For me, the fundamentals of genetics are that we are interested in phenotype and that results from the combination of genotype and the environment. That is, phenotype is equal to the genotype plus the environment (P = G + E) ... The trouble with emphasising [Mendelian classical] principles in the beginning is that students don't see the role of the environment in them, whereas in fact, there is nothing external in humans that is simply inherited with no environmental influence, despite what the textbooks say.Expert 5: The structural unit, to me, is every bit as important as how that gene functions with the phenotype and how that phenotype then interacts with the environment.
Expert 2: I tell the students that these alleles are operating on a genetic background; they don't operate on their own. This means that the same allele in different people can have slightly different effects as they are operating on a different background, in a different environment.
Trumbo (2000) explains that the ability of humans to create novel environments, such as the life saving diets given to people with the genetic disorder PKU (phenylketonuria), means that we can look to genetics as an important contributor to the well being of an organism, not as fate. Education is the key to taking advantage of such technologies and understanding the effects of the complex relationship between genetics and the environment on the development of an organism. Trumbo criticises current biology curricula in the way that genetic and environmental effects are divorced from one another and not presented as cooperating factors that shape characteristics.
Theme 4: Gene expression is controlled
The fourth theme that became evident in the discussion with experts was that there are parts of the DNA that control gene expression.
Expert 3: One other thing that isn't touched on at school is the fact that not every gene is expressed in every cell.Expert 9: To understand the molecular mechanism of the determination of characters you have to understand biosynthesis. It is also important to understand that genes are switched on and off at various times in the ontogeny-that should be explained to children at the outset.
Expert 1: It [the gene] also has parts responsible for regulating its own expression.
Fox-Keller (2000) commits a whole chapter to exploring the issue of gene expression and the question of how organisms are made. She claims that the metaphor of a 'genetic program', first introduced by Jacob and Monod, creates a marked distinction between classical and molecular genetics because it provides a fundamental explanatory concept for biological development. She comments that all animal genes are essentially the same: what makes the differences between species is the structure of gene networks, regulatory mechanisms and gene expression. It is the regulatory dynamics of the whole cell and not simply the gene regulating itself, that signals which protein a gene should make and under what circumstances (Fox-Keller, 2000). This means that the gene is not independent and unaffected by the environment in which it is embedded.
While Fox-Keller promotes the metaphor of a genetic program, Tudge (1993) claims that the blueprint metaphor for the genome is potentially a misleading myth because genes are not passive bystanders in the life of cells. From an education perspective, it is interesting to tease out what is different between these metaphors. A blueprint metaphor suggests that the genetic plan is static and unchanging and that there is a one-way flow of information from the blueprint to the thing being constructed. In other words, it conveys the message that the cell makes exactly what the blueprint genome says. In contrast, the program metaphor conveys a message that the genome is more a plan of action or system of procedures and activities that can be enacted at different times or in concert as necessary. A program can be modified depending on the context in which it is set into action and this implies that the genetic program is more open to variation depending on the cellular environment. The program metaphor suggests a process that is more fluid and responsive in nature that produces a product that is less rigid in makeup compared with the blueprint metaphor. In genetic terms, the program metaphor is less deterministic than the blueprint metaphor.
Tudge's (2000) message that, 'simplicity should not be confused with crudity, or complexity with profundity' (p. 286) is a perfect summary of what this article reveals for teachers of high school, biology. The message that emerges from this exploration of the concept of the gene is that the complexity of genetics is possibly not helpful in the education of everyday citizens. Simple, but accurate, messages that reflect, the profundity of genetics are what teachers should strive for in educating the populace. Tudge (2000) claims that the general picture of life's controls that emerged by the end of the twentieth century is remarkably simple and tidy.
"'DNA makes RNA makes protein", and proteins of course (mainly in the form of enzymes), are the body's functionaries, which effectively run the show' (p. 138). By 'run the show', Tudge means that proteins are essential in many aspects of living things. For example, proteins are essential for the structure of organisms, for metabolism in the form of enzymes, for communication in the form of hormones, and they form the defensive forces of living things as antibodies. Perhaps teaching high school students about proteins is more important than teaching about genes? Indeed, Morange (2001) says that, '... if molecular biologists had to designate one category of macromolecules as being essential for life, it would be proteins and their multiple functions, not DNA and genes' (p. 2). As suggested in the beginning of this paper, however, the concept of the gene will remain a central explanatory aspect of biology in the future. This means that high school teachers must aim to enable students to use an appropriate concept of the gene as part of their scientific literacy.
The exploration presented in this paper provides a window into the kinds of conceptual changes that are likely to be necessary for students to develop a concept of the gene that is appropriate in the age of biotechnology. The following five simple messages could be the cornerstone of any introductory genetics course and can be developed to varying degrees with a range of students.
1. Contrary to popular belief, genes acting alone do not usually determine characteristics and behaviours.
2. Genes are made of DNA, which is a chemical code for making polypeptides which form proteins.
3. Proteins are very important biological molecules that affect a complex array of functions in living organisms including development and behaviour.
4. The characteristics and behaviour of living organisms are determined by a complex interaction of their genetic make-up and the environment in which they live.
5. Development is the result of the genome acting like a genetic program.
Falk, R. 1986. "What is a gene?" Studies in the History and Philosophy of Science 17(2):133-173
Fox-Keller, E. 1983. A feeling for the organism: The life and work of Barbara McClintock. New York, W. H. Freeman and Company
Fox-Keller, E. 2000. The century of the gene. Cambridge, MA, Harvard University Press
Lewis, J. and Kattmann, U. 2004. "Traits, genes, particles and information: Revisiting students' understanding of genetics." The International Journal of Science Education, 26(2):195-206.
Nelkin, D. and Lindee, M. S. 2004. The DNA mystique: The gene as a cultural icon. Michigan: The University of Michigan Press
Morange, M. (translated by M. Cobb). 2001. The misunderstood gene. Cambridge, MA, Harvard University Press
Portin, P. 1993. "The concept of the gene: Short history and present status." The Quarterly Review of Biology 62(2):173-223
Trumbo, S. 2000. "Introducing students to the genetic information age." The American Biology Teacher 62(4):259261
Tudge, C. 1993. The engineer in the garden. London: Jonathan Cape
Tudge, C. 2000. In Mendel's footnotes: An introduction to the science and technologies of genes and genetics from the 19th Century to the 22nd. London: Jonathan Cape
Venville, G. and Treagust, D.E. 1998. "Exploring conceptual change in genetics using a multidimensional interpretive framework." Journal of Research in Science Teaching, 35(9):1031-1055
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