Behavior Genetics PDF

MODULE- II BEHAVIOR GENETICS STRUCTURE 2.1 Introduction 2.2 Meaning and Definition of Behaviour Genetics 2.3 Nature and Scope of Behaviour Genetics 2.4 History of Behaviour Genetics 2.4.1 First Single-Gene Variants...

MODULE- II BEHAVIOR GENETICS STRUCTURE 2.1 Introduction 2.2 Meaning and Definition of Behaviour Genetics 2.3 Nature and Scope of Behaviour Genetics 2.4 History of Behaviour Genetics 2.4.1 First Single-Gene Variants 2.4.2 Enter the Fly 2.4.3 First Strain Differences 2.4.4 First Selection Experiments 2.4.5 Genetics and Eugenics 2.4.6 The Emergence of Quantitative Behavioral Genetics 2.4.7 First ‘Genetic Dissection’ Of Behavior 2.5 Research Methods in Behaviour Genetics 2.5.1 Animal Studies 2.5.2 Family Studies 2.5.3 Twin Studies 2.5.4 Adoption Studies 2.5.5 Combined Studies 2.5.6 Linkage Analysis 2.5.7 Association Studies 2.6 Behaviour and Genetics 2.6.1 The Influence of Genes on Behavior 2.6.2 Behavioral Genetics 2.6.3 Classical Genetics 2.6.4 The Influence of Behavior on Genes 2.7 Eugenics 2.7.1 Early History 2.7.2 Eugenics Organizations and Legislation 2.7.3 Popular Support for Eugenics 2.7.4 Anti-Eugenics Sentiment 2.8 Genetic Engineering 2.8.1 Historical Developments 2.8.2 Process and Techniques 2.8.3 Controversy 2.9 Summary 2.10 Questions LEARNING OBJECTIVES:  To Understand the basic principles of genetics and its use in the study of behavior  Evaluate evidence that behavioral characteristics are influenced by genetics and consider the implications of genetic knowledge in psychology.  To have a clearer understanding of the contribution that genetics make to individual differences in behavior. 24 2.1 INTRODUCTION Why do humans range so widely in their susceptibility to mental illness, in their willingness to take risks, and in their performance on intelligence tests? One answer to this question comes from scientists in the field of behavioral genetics. They say that the variation in behavioral traits across a population is due, in part, to the genes. So many studies have pointed to connections between genes and behaviors that most scientists now feel comfortable stating that there is such a link for every possible behavior. But what does it really mean to say that there is a link between genes and behavior? Does it mean that there is a gene that makes some of us blush when embarrassed; that there is one gene that makes you prefer classical music and another gene that makes you dislike it; that there is a bunch of genes that each provides for various levels of skill in playing poker? The answer to all these questions is no. Does it mean behavior passes down from generation to generation, i.e., is inherited, just like baldness and eye color? Again, the answer is no. The pervasive role of genes in behavior does not mean what it is commonly misunderstood to mean. It does not mean that a gene or even several genes can make you act in any way. It does not mean that a behavior can “pass down through the genes.” Such claims are not accepted in behavioral genetics. Behaviour genetics, also called psychogenetic, the study of the influence of an organism’s genetic composition on its behaviour and the interaction of heredity and environment insofar as they affect behaviour. The question of the determinants of behavioral abilities and disabilities has commonly been referred to as the “nature-nurture” controversy. Behavioral genetics is the study of genetic and environmental influences on behaviors. By examining genetic influence, more information can be gleaned about how the environment operates to affect behavior. 2.2 MEANING AND DEFINITION OF BEHAVIOUR GENETICS Behavioral (or behavior) genetics is a field of study concerned with the genetic (inborn) and situational (from the environment) influences on behavior. It is essentially the study of the 'nature vs, nurture' debate. The goal in behavioral genetic research is to identify which behaviors are influenced by genes and which are mostly influenced by the environment and situational factors. Behavioural genetics is the interdisciplinary effort to establish causal links between genes and animal (including human) behavioural traits and neural mechanisms. Methods used include twin studies, quantitative trait mapping by linkage to allelic variants, transgenic animals and targeted gene disruption or silencing. This field studies the connections between genes and behavior. Human behavior genetics is a subset of behavioral genetics that researches influences on human behavior. Twin studies are commonly used in behavioral genetics research because they are ideal for teasing apart genetic and environmental influences. 2.3 NATURE AND SCOPE OF BEHAVIOUR GENETICS We focus on four areas of research in behavioural genetics: research into intelligence, personality traits, antisocial behaviour and sexual orientation. These were selected to illustrate the range of topics that are being investigated, and because of the critical issues they raise. 25  Intelligence is a complex phenomenon and there is considerable debate about whether it can be measured effectively. There is substantial disagreement regarding the extent to which genetic and environmental factors influence intelligence.  Personality traits have been studied by psychologists for many years. Five core traits have been the focus of research in both psychology and behavioural genetics: neuroticism, introversion/extraversion, openness, agreeableness and conscientiousness.  Antisocial behaviour is classified differently by mental health clinicians, criminologists and psychologists, but a common factor is that it is behaviour which violates the rights and safety of others. It includes traits such as aggression and violent behaviour.  Sexual orientation is regarded by some as a matter of choice and by others as a matter of biology. What role, if any, do genetic factors play in sexual orientation? The answer to this question is bound to influence the way in which people react to homosexuality. 2.4 HISTORY OF BEHAVIOUR GENETICS Francis Galton is often cited as the first behavioral geneticist. Stimulated by reading his cousin Charles Darwin’s Origin of Species, he began to survey the concentration of abilities and accomplishments in families. Using the newly developed statistical analysis of quantitative characteristics in populations that he had developed, Galton published the first study claiming to trace inheritance of behavioral traits. His failure to consider non-hereditary factors in the familial clustering’s that he saw has discredited his findings in the eyes of modern researchers, and his promulgation of eugenic ideology has colored his subsequent treatment by history. His views, however, were entirely consistent with 19th century hereditarianism. Despite these contemporary reservations, Galton stands as the starting point in the long road towards understanding the relation between heredity and behavior. 2.4.1 First single-gene variants With the advent of Mendelian genetics at the turn of the 20th century and its application to animals, some early attempts were made to trace the inheritance of behavioral traits. Few of the initial efforts were directed at understanding behavior. For the most part, they used behavioral phenotypes as tests of Mendelian inheritance. Mouse strains with characteristic whirling behavior, known as ‘Japanese waltzing’ mice, were well known during this period as popular curiosities available from pet dealers. Arthur D. Derbyshire at Oxford University performed an early experiment to test for Mendelian inheritance of waltzing behavior. He observed that waltzing was recessive but concluded from the failure to match the expected 3:1 ratio in the F2 (97 waltzes to 458 non-waltzes) that its inheritance did not support a Mendelian model. This is an early case of being misled by pleiotropic effects of a mutation: he failed to consider the possibility of reduced viability of the homozygotes, a common feature of neurological mutants. (Nine years later, when Alfred Sturtevant hit upon the idea of recombination between mutations as indicative of a linear arrangement of genes on the chromosome, he was unperturbed by his much more significant deviation from an expected Mendelian ratio; he was already sold on the idea of Mendelian traits.) Work on putative single-gene variants in humans was pioneered by Charles B. Davenport at Cold Spring Harbor. These studies suffered, however, from Davenport's propensity to see Mendelian inheritance in every trait he looked at, from Huntington's Disease (which he 26 correctly pegged as an autosomal dominant), to feeble-mindedness (which he claimed was recessive, but we now suspect to be environmentally induced by prolonged contact with academic researchers). Davenport's assumption, appropriate for the day, was that human behavior is determined through and through by ‘unit characters’ of heredity — single-gene Mendelian factors that are wholly responsible for the determination of a trait. This illustrates a scientific trait that we have seen reemerge in the current genomic era: the tendency to account for all unknowns by a newly discovered source of insight. 2.4.2 Enter the fly The fruit fly Drosophila melanogaster made its research debut in the laboratory of William E. Castle at Harvard University in 1901. This was the first laboratory to pursue the newly propounded principles of Mendelian genetics in animals, concentrating primarily on the coat color genetics of guinea pigs and rats. In parallel with these mammalian studies, however, Castle took the suggestion of his entomologist colleague C.W. Woodworth and began breeding studies with the fruit fly, testing how well it tolerated inbreeding, selection, and probing some of its simple behavioral responses. The first paper on the subject was a study in 1905 by Castle's student F.W. Carpenter on the fly's phototactic, geotactic and metabosensory responses. He found that flies are positively phototactic, negatively geotactic, and induced to move by mechanical stimulation. In 1906, Castle and his students published their major work on the fly, in which they demonstrated that it tolerated inbreeding to a considerable extent and that it could be selected for improved fertility. Other Castle students soon followed with the first study of olfactory behavior in Drosophila, showing that flies like amyl or ethyl alcohol and acetic or lactic acid, and that they find food primarily by smell. The first study of anataxis (sensitivity to wind currents) showed that flies respond negatively. None of these behavioral studies involved the use of genetic variants and one may wonder where the idea came from to look at these behaviors. The most likely influence was the German zoologist Jacques Loeb, who had moved to the United States and became a key figure in establishing the University of Chicago as one of the first research universities in 27 America. Loeb's research on tropisms in Planaria were well known to all zoology students and is referenced in these early Drosophila papers. Another first in Castle's lab was the study by his student F.E. Lutz in which flies were selected over more than 40 generations for variation in wing-vein morphology. He also carried out experiments on mating preferences among the various lines, including experiments in which he cut off the male sex combs. The rationale for these mating experiments was framed in the context of Darwin's discussion of sexual selection: had he created reproductively isolated strains? In his description of the work, Lutz makes the first, fateful reference to the richness and detail of this fly behavior: “There is an elaborate ‘courtship’, in which the flirting of the wings in front of the prospective mate plays a large part. It appears a choice were made based on sight, but I doubt whether that is the case. However, there is no doubt of the choice.” T.H. Morgan's ‘Fly Room’ at Columbia was the scene of the first studies of genetic variants in Drosophila, which soon became a cottage industry of gene mapping. The two behavioral studies that were produced in this initial period followed on the initial reports from Castle's group. A.H. Sturtevant inaugurated the study of genetic variants affecting courtship behavior, as well as the comparison of species differences. He made several key observations that have since been elaborated upon: that males use their wings to stimulate females; and that light (vision) is unnecessary for courtship (in D. melanogaster). In the first courtship studies with genetic variants, he tested for mating preference within and between mutant lines and made the first observations on male/female mosaic animals (gynandromorphs) that demonstrated the separability of attractiveness from propensity to perform courtship. Another Morgan student, R.S. McEwen, studied phototropic and geotropic responses in the fly. He subsequently reported the first behavioral abnormalities in mutants: poor phototaxis in the cuticle pigment mutant tan and in the wing morphology mutant vestigial. It is fitting that these first two reports of mutant defects were in obviously pleiotropic mutants, thus foreshadowing the course of behavioral mutant studies to come. In the 1960s, Seymour Benzer would stumble upon these same mutants in his inaugural studies of photo taxis, but otherwise the testing of fly mutants for behavioral anomalies lay fallow for many years. It is not clear what motivated McEwen to examine behavior in these mutants — certainly not testing for Mendelian segregation; that had already been done in Morgan's lab for the mutants' morphological phenotypes. His work did follow from earlier studies of the response of wild-type Drosophila to light and gravity 6, 9, and was firmly rooted in the tradition of Jacques Loeb's influential ideas on animal tropisms. In this sense, he was the first to test mutants for behavioral defects. 2.4.3 First Strain Differences The first study of strain differences in behavior traces back to one of the original animal behaviorists, Robert Yerkes, who compared tame rats with wild rats differing in such observable traits as biting, teeth gnashing, jumping, hiding, urination, defecation, cowering, and so on. He then went on to analyze F1 and F2 generations and found no simple Mendelian segregation of traits. The F1s showed relatively high behavioral scores, but the F2s were lower and much more variable. A similar study in mice gave correspondingly comparable results. Though not analyzable at the time, the results foreshadowed what would become the mantra for studies of strain differences, and eventually for any kind of selected phenotype: the effects were genetically complex. 28 2.4.4 First Selection Experiments The aforementioned early breeding experiments in Drosophila by Castle and his students had as a principal goal the establishment of laboratory strains with high fertility and tolerance of inbreeding; hence, their 15 generations of selection. Lutz's experiment on wing-vein morphology went on for over 43 generations. A contemporary experiment was carried out by F. Payne in which flies were raised for 69 generations in the dark. Both Lutz and Payne were interested in the question of whether disuse over many generations could cause structures to degenerate — wings in the case of Lutz, and eyes in the case of Payne. In neither case was there any evidence for such an effect. Animal husbandry's experience in selective breeding for traits was a cornerstone of Darwin's observations in developing his theory of natural selection and had been universally acknowledged through the ages as indicative of the inheritance of parental characters by their offspring. The science of analyzing selectively bred behavioral traits began with E.C. Tolman at Berkeley in the 1920s, and with it arose the first authentic school of thought devoted to the study of the relationship between heredity and behavior. Rats were tested for maze-running ability followed by mating of the brightest to each other and likewise mating of the dullest to each other. Similar multi-generational selection was subsequently carried out by Tolman in collaboration with R.C. Tryon, who went on to analyze inheritance patterns of maze-running ability in F1 and F2 progeny after 18 generations of selection and concluded (you guessed it) that the inheritance was genetically complex. Maze learning was not the only behavior that responded to selection in rats or mice. Activity versus inactivity and emotionality versus non-emotionality were also selected in multi- generational paradigms, and also shown to be genetically complex. 2.4.5 Genetics and Eugenics The 1920s saw the maturation of genetics into a mature scientific discipline, but it was also the heyday of eugenics — a movement that saw the future salvation of humanity in scientifically planned selective breeding 2, 3, 5. Started by Galton and championed by Davenport, eugenics spread widely in England and America to the point that county fairs would host booths to promulgate ‘social hygiene’ through ‘fitter families’ and ‘better babies’ contests (Figure 3). The movement had its dark advocates, such as Davenport, who saw great threats to the genetic stock of Americans in the waves of new immigrants from eastern and southern Europe, and more ‘progressive’ advocates, such as Hermann Muller, who espoused some more optimistic eugenics aimed at improving the health of humanity. Most of practicing geneticists, however, saw little justification in the wholesale ascribing of all human behavior to simple Mendelian factors. Morgan's fly work had already begun to turn up complexities and pleiotropies in many of the genes they studied. But nearly all scientists felt strongly that wading into the political waters was beneath them, even as the U.S. Congress held hearings on the need for a national origins quota system. Quotas were eventually written into the Immigration Act of 1924, thus ending the great wave of American immigration. Notable exceptions to this scientific reticence were J.B.S. Haldane in England and the protozoologist H.S. Jennings, who distinguished himself as the only American geneticist willing to testify before Congress and challenge the scientific basis of the anti- immigrant claims. The anti-immigrant sentiment that fueled the eugenics movement is visible today in the debates over immigration policy, but the lack of effective opposition back then can be 29 ascribed in large measure to the absence of countervailing explanations. The social sciences of anthropology, sociology, and behaviorism were in their infancy at the time, and there simply was no concept of culture or environmental influence to stand up against long- standing hereditarian assumptions 3, 5. Nurture was out. 2.4.6 The Emergence of Quantitative Behavioral Genetics Just as the new science of Mendelian genetics was quickly seized upon for studies of the inheritance of behavioral traits at the turn of the 20th century, so the advent of quantitative genetics several decades later sparked a new discipline and mode of analysis for behavioral traits with complex modes of inheritance. The analytical techniques developed by Fisher, Wright and Haldane, so crucial in reconciling Mendelian genetics with Galtonian quantitative traits, began to be applied to behavioral traits, such as those seen in selected lines or in strain comparisons. Aside from the ability to model and estimate the number of loci involved, based on the phenotypic distributions in F1, F2 and backcross progeny, the analysis also afforded an estimate of the number and nature of gene interactions. The problem of the heritability of a behavioral trait in Drosophila, and whether it could be assigned to a single gene, seems first to have been addressed by J.P. Scott at Wabash College in Indiana. He recognized that a behavioral difference between wild-type flies and white or brown mutants might not be due exclusively, if at all, to the visible mutations if the strains contained other differences in genetic background. He tested this by crossing wild-type alleles of white or brown into the original genetic background of the mutants and demonstrated that the background genotypes did exert significant effects. Jerry Hirsch was the pioneer who brought quantitative genetic analysis to the study of behavior. As a student in Tryon's lab, he began selection experiments for geotaxis preference in Drosophil), which he continued with Dobzhansky at Columbia and then for many years thereafter at U. Illinois (reviewed in). In addition to the standard litany of F1, F2 and backcross experiments, Hirsch also introduced the first truly genetic technique into the mix: chromosome analysis. This technique capitalized on the ability in Drosophila to manipulate and track the segregation of whole chromosomes without the complication of recombination, first developed by H.J. Muller. As a result, individual chromosomes from a selected line could be isolated onto a neutral genetic background and tested for their relative contribution to the phenotype. In addition, interactions between the set of loci on different chromosomes could be tested directly, albeit not individually. He also promulgated Tryon's idea of population diversity in behavioral analysis — the concept that individuals in a population are behaviorally variable as part of that population's Darwinian repertoire. Hirsch epitomized the approach of those studying ‘genetic architecture’. The philosophy of this approach can be summarized as follows: characterize quantitatively a behavioral phenotype in a given population (strain), whether a natural population or a strain resulting from artificial selection and infer its genetic architecture (number of responsible genes and their interactions) from the analysis of the phenotype and its variance in sets of progenies from test crosses between different populations (strains). The consistent conclusion from nearly all of Hirsch's (and everyone else's) studies of the genetic architecture of behavior is that it is complex and multigenic. 2. Hirsch's work represented a first attempt at reinstating the relevance of genetic influences to the study of behavior. As described above, the high-water mark of the eugenics movement occurred in the 1920s, only to subside with the rise of the social sciences. No school of 30 thought was more influential in replacing hereditarian thinking than behaviorism, most closely associated with the psychologist John B. Watson. Watson and his student B.F. Skinner promulgated a scientific view of human nature diametrically opposed to genetic determinism, epitomized by Watson's assertion: “Give me a dozen healthy infants, well- formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select — doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors.” With the ascendant social sciences, the dominance of behaviorism, and revulsion at the atrocities associated with the Nazi version of eugenics, the 1950s represented the low ebb for hereditarian explanations of behavior. Genes were irrelevant; nature was now out. Hirsch's effort to win recognition for the role of genes was based on his recognition that behavior had to be understood in the context of evolution, a concept that goes back to Darwin and which had been revived in the 1920s in the ethological work of Nikolaas Tinbergen and Konrad Lorenz. By introducing the element of population genetics, Hirsch brought the modern evolutionary synthesis to behavioral studies. 2.4.7 First ‘genetic dissection’ of behavior Up to this point, the only conclusion that one could draw from studies of heredity and behavior was that aspects of the phenotype could be affected by genotype. Some of the first steps in the direction of genetic dissection of behavior were taken in studies of phototaxis and optomotor response. Brown and Hall at the University of Illinois studied white and Bar mutants' phototactic responses. They systematically studied the effects of varying light intensity and wavelength, generating data on the threshold of a fly's response as well as an action spectrum. By counting facets in Bar versus normal flies, they were also able to demonstrate a correlation between surface area of the eye and speed and sensitivity of response. Hans Kalmus of University College London used mutants to test for the functional components necessary for the optomotor response. He built on a behavioral assay developed ten years earlier by two of the pioneers in vision science, who were neither fly biologists nor geneticists: Selig Hecht at Columbia, the premier biophysicist of vision in his day, and his student George Wald, who later went on to identify rhodopsin and describe the photochemical cycle of visual pigment excitation and regeneration. Hecht and Wald measured responses of Drosophila to moving stripes — the ‘optomotor’ response — testing different stripe widths and different intensities of illumination to determine the flies' visual acuity. Perhaps the fact that Hecht had been recruited to the Zoology Department at Columbia University by T. H. Morgan prior to the departure of the fly group ten years earlier, and that Jack Schultz had spent time in his lab learning to isolate photopigments from the fly, had something to do with the choice of Drosophila for these studies. In the paper, they claim that flies were used because of their genetic uniformity (for a change) and their year-round availability. Following Hecht and Wald, an extensive and detailed investigation of visual acuity and the optomotor response was conducted by Lotte von Gavel at the University of Königsberg, and then by Kalmus who showed, not surprisingly, that eyeless flies have no optomotor response, and that Bar-eyed flies, with a reduced number of ommatidia, have a correspondingly reduced optomotor response. More significantly, Kalmus reported that white-eyed flies failed to respond to stripe movement, despite their normal phototactic behavior. He attributed this 31 (correctly, as it turns out) to the loss of the screening pigments between ommatidia. This line of research was resumed twenty years later by Karl G. Götz at the Max-Planck Instituter Kybernetik in Tübingen with a more sophisticated and analytical approach to the optomotor response. 2.5 RESEARCH METHODS IN BEHAVIOUR GENETICS 2.5.1 Animal studies Basic genetic research on fruit flies started more than 100 years ago, but the classic study on behavior dates to the 1950s. Researchers noticed that if you put fruit flies in a tilting maze, some would crawl upward, and others would crawl downward. This tendency to move with or against gravity is called geotaxis. The researchers selected fruit flies that preferred to move uphill and bred them together and did the same for fruit flies that preferred to move downhill. When after many generations they had created strains of fruit flies that consistently responded to gravity in the same way, the researchers were able to conclude that there was a genetic basis to geotaxis. This selective breeding experiment contributed early evidence to the claim that heredity plays a role in behavioral traits. Another method is to create inbred strains. These are whole populations of genetically near- identical animals that have been created by mating brothers to sisters for several generations. (In recent years researchers have learned how to make inbred strains through cloning.) Researchers look for variations in behavior between different inbred strains reared in identical environments, as evidence of genetic components to behavior. They also look for variations in behavior within inbred strains. Since members of an in-bred strain are genetically alike, observed differences in behavior can be attributed to pre- or postnatal environmental causes. 2.5.2 Family studies A fundamental experimental method involving humans is the family study. This starts with one person, called the proband, and the focus is on one trait possessed by that person. The proband’s family tree (pedigree) is drawn up to include first-degree relatives (parents, siblings, and children) and sometimes also second-degree relatives (aunts, uncles, grandchildren, grandparents, and nephews or nieces), plus even more distant family members. The members of the family tree are looked at to see who, if anyone, has the trait identified in the proband or related traits. This type of study can reveal whether the trait runs in the family. It does not explain why. Both genes and environment are implicated because the members of a biological family are similar genetically and tend to live in similar environments. However, it is sometimes possible to get a clue about cause from a family study. For example, if a proband has a trait in common with first-degree relatives and with more distant relatives, the possibility is raised that the cause comes from the environment shared by the family rather than shared genes. 2.5.3 Twin studies In twin studies, researchers actively recruit living twins. They observe the twins’ behaviors, give them personality tests, interview them, and ask them to fill out surveys. Researchers also extract data on twins from existing databanks, such as records on hospital patients or members of the armed forces. 32 Twins are two offspring produced by the same pregnancy. Twins can either be 1. Monozygotic (identical) 2. Dizygotic (fraternal) Monozygotic (MZ) or identical twins occur when a single egg is fertilized to form one zygote which then divides into two separate embryos. Monozygotic twinning occurs in birthing at a rate of about 3 in every 1000 deliveries worldwide. Identical twins share the same genotype, since their genomes are identical; but they never have the same phenotype, although their phenotypes may be very similar. Another cause of difference between monozygotic twins is epigenetic modification, caused by differing environmental influences throughout their lives. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few epigenetic differences. The number of epigenetic differences increases with age. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference. Dizygotic (DZ) or fraternal twins usually occur when two fertilized eggs are implanted in the uterus wall at the same time. Male–female twins are the most common result, 50 percent of dizygotic twins and the most common grouping of twins. The genetic similarity between dizygotic twins is, on an average 50 percent. Female–female dizygotic twins are sometimes called "sororal twins". Dizygotic twinning ranges from 6 per 1000 births in Japan (similar to the rate of monozygotic twins) to 14 and more per 1000 in some African countries. Factors that increases the likelihood for woman to naturally conceive twins or multiples Mother's age: women over 35 are more likely to have multiples than younger women. Mother's use of fertility drugs: approximately 35% of pregnancies arising through the use of fertility treatments such as IVF involve more than one child. 33  Younger patients who undergo treatment with fertility medication containing artificial FSH, followed by intrauterine insemination. Intelligence The IQ scores of fraternal twins are more alike than those of ordinary brothers and sisters. The correlations between IQ scores of fraternal twins are 0.86 while that of siblings are 0.41 when they are reared together. Two previous studies of fraternal twins reared apart have yielded a mean-weighted heritability estimate of 0.38. The correlations between IQ scores of identical twins are 0.86 (reared together) and 0.72 (reared apart) Psychologists who emphasize genetic believe figures that like these show that differences in adult intelligence are roughly 50% hereditary (Casto, DeFries & Fulker, 1995). However, strong evidence for environmental view of intelligence comes from families having one adopted child and one biological child. Studies showed that children reared by the same mother resemble her in IQ to the same degree. It doesn’t matter whether they share her genes. (Kamin, 1981; Weinberg, 1989) Personality Traits Hereditary is responsible for about 25 to 50 percent of the variation in many personality traits ( Jang &Livesley, 1998; loehlin et.al., 1998) For two decades, psychologist at the University of Minnesota have been studying identical twins who grew up in two different homes. Medical and psychological tests reveal that reunited twins are very much alike, even when they are reared apart ( Bouchard, 2004; Bouchard et.al., 1990) Twin studies in criminals Epidemiological evidence that genetic factors contribute to criminal behavior come from three sources: family, twin, and adoption studies. Twin studies compare the rate of criminal behavior of twins who are genetically identical or monozygotic twins (MZ) with twins who are not, or dizygotic twins (DZ) in order to assess the role of genetic and environmental influences. To the extent that the similarity observed in MZ twins is greater than that in DZ twins, genetic influences may be implicated. Using an unselected sample of 3,586 twin pairs in Denmark, Christiansen reported 52 percent of the monozygotic twins were concordant for criminal behavior whereas only 22 percent of the dizygotic twins were concordant for criminal behavior. A marked increase of concordance for criminal behavior among monozygotic twins suggests that the MZ twins in herit some biological characteristic(s) that increases their joint risk for criminal involvement. Twins Reared Apart Grove and others investigated the concordance of antisocial problems, as measured by the Diagnostic Interview Schedule (DIS), among a sample of thirty-two sets of monozygotic twins reared apart (MZA) who were adopted by nonrelatives shortly after birth. Grove found substantial overlap between the genetic influences for both childhood conduct disorders (correlation of.41) and adult antisocial behaviors (correlation of.28). 34 Twin Escalation Syndrome The term Twin Escalation Syndrome, is defined as the tendency of multiples to intensify and expand their behaviors in reaction to each other. Advantages of Twin Studies  Identical twins have essentially identical DNA. Therefore, it seems likely that any differences between twins will have to be caused by environment rather than by genetics.  It is also possible to make twin studies more robust by differentiating between identical and fraternal twins.  For example, imagine that a study shows that a large percentage of identical twins share a common trait while a much smaller percentage of fraternal twins do. This would strongly imply that genes have a great deal to do with this particular trait.  Disadvantages Twins are not terribly common and identical twins are even less so. The low number of possible subjects for the studies and the fact that they may not be representative of the overall population. It is possible that there are differences between twins and the population as a whole. If this is the case, studies of twins may yield results that are more applicable to twins than to other people. 2.5.4 Adoption Studies Adoption studies look at biologically related people who have been reared apart. One method is to compare identical twins adopted into separate homes, that is, into measurably dissimilar environments. The disparate environments are assumed to shape them differently so that similarities in traits are attributed, at least in part, to genetic effects. Another method compares adopted children to both their biological and adoptive parents. Evidence for partial genetic influence on a trait is found when adoptees are more similar for the trait to their biological parents than to their adoptive parents. Evidence for some environmental influence is found when the adoptee is more like his or her adoptive parents than the biological parents. Yet another adoption method is to compare adopted children to other children in the family who are biological offspring of the parents. Similarity found here would suggest environmental effects for the trait under investigation, while dissimilarity would suggest genetic effects. Adoption studies are not as numerous as family or twin studies because subjects are hard to find, especially given the decline in within-nation adoption over the past several decades. Also, in countries such as the United States where adoption records are confidential, it can be difficult for researchers to get accurate information about the biological parents. 2.5.5 Combined studies We have described family, twin, and adoption studies as distinct types of research, but in practice they can overlap. As just noted, an adoption study might look at pairs of twins that had been adopted away into different families. Some studies have unusual permutations, for example, a family study might include stepchildren who are related to one but not both parents. 35 Furthermore, data from all three kinds of studies can be pooled together. This kind of undertaking, called meta-analysis, attempts to extract more meaning out of data that have been generated by multiple studies of the same trait. In a mathematical exercise called model fitting, several plausible explanations, in the form of mathematical formulas, are proposed that express the relative contributions of genetics and environment to the variance for a trait. The combined data are plugged into each model to see which one best explains the variance. One of the problems confronted by model fitters is that different studies might use different diagnostic measures to identify those who have or do not have the trait under study. For example, a subject who is gauged as “highly religious” in one study might not be so categorized in another. Therefore, researchers must assume degrees of error and hope that the signal outweighs the noise. Today, researchers attempt to be consistent with each other in their data collection methods. They collaborate on diagnostic measures and study designs with the intention of eventually pooling their data for meta-analysis. Several such projects are underway involving teams across the country and around the world. These studies are investigating schizophrenia and other mental illnesses, alcoholism, autism, and many other behavioral disorders. 2.5.6 Linkage analysis The traditional way that behavior has been studied by geneticists using twin, family, and adoption studies is referred to as quantitative research, because the objective is to identify how behavioral traits vary by degree (quantitatively) in individuals in a population. Molecular research, which probes at the DNA level, complements this classical approach. Such research makes use of the tremendous computing power that has come about in recent years. It also takes advantage of the completed drafts of human, animal, and insect DNA sequences achieved through the Human Genome Project and related ventures. Linkage analysis relies on the fact that chromosomes are paired. In germ cells, the two chromosomes in a pair commonly exchange genetic material before the full complement of chromosomes splits in half to create the sperm and egg cells of reproduction. This exchange is called recombination or crossing over. Recombination is a normal exchange process, unrelated to mutation that enhances genetic diversity. It creates new combinations of alleles on each chromosome. In classical linkage analysis, researchers collect data on two variables from family groups. The first variable is the trait being researched. The second variable is called a genetic marker. This is a gene whose precise location on a chromosome is already known. For each family member, researchers record whether and to what extent the trait is present and which allele for the marker gene is present. They note how often the trait and any allele for the marker gene are inherited together. Where a pattern of frequency occurs, this suggests that the gene for the trait is near the marker gene (“linked”) because the combination of alleles for the two genes (haplotypes) is not being broken apart in recombination. Researchers make statistical calculations from their data to come up with an old score (“old” stands for “logarithmic odds” or “likelihood of odds”). The higher the old score, the higher the probability that the two genes are close by on the same chromosome. Researchers do this type of analysis with several families. They also look for linkage between the gene for the trait under study and several different marker genes. The first tactic helps 36 them confirm linkage and the latter tactic helps them better target the approximate location along the chromosome of the trait-related gene. 2.5.7 Association studies Another molecular research route is the association study. This focuses on a single gene that has already been isolated, the candidate gene. Through the association study, researchers seek to identify whether the variation in this gene’s alleles might be statistically associated with variation in a trait. DNA samples are taken from subjects who have the trait and a similar number of subjects (a control group) without the trait. Each subject’s DNA is genotyped to see which allele is present at the genetic locus under study. A statistical test is then conducted to see if any allele shows up more frequently in subjects with the trait compared to subjects without the trait. Association studies have two advantages over linkage analysis. First, they require a smaller number of subjects who do not have to be related. Second, they can help identify specific genes, not just chromosomal regions. This moves researchers that much closer to the next step, which is to figure out how specific genes correlated with a trait contribute to the biological processes underlying that trait. The complete mapping of the human genome has helped researchers find candidate genes on which to focus their research using the association method. Animal studies also have helped identify good targets for association studies using human subjects. The quantity of association studies churning out from research labs in recent years has been described as a “veritable cascade.” These studies cover a broad spectrum of diseases and traits - Parkinson’s disease, multiple sclerosis, restless leg syndrome, smoking behavior, and migraines, to name just a few. 2.6 BEHAVIOUR AND GENETICS Chromosomes are structures in the nucleus of a cell containing DNA, histone protein, and other structural proteins. Chromosomes also contain genes, most of which are made up of DNA and RNA. DNA, or deoxyribonucleic acid, determines whether our eyes are blue or brown, how tall we will be, and even our preference for certain types of behavior. Known as our “genetic code,” it is shaped like a double helix, made of sequences of nucleic acids attached to a sugar phosphate backbone. Genes are subsections of DNA molecules linked together that create a characteristic. Each chromosome is made up of a single DNA molecule coiled around histone proteins. Research dating back to the 1800s shows that every living creature has a specific set of chromosomes in the nucleus of each of its cells. Human chromosomes are divided into two types—autosomes and sex chromosomes. Some genetic traits are linked to a person’s sex and therefore passed on by the sex chromosomes. The autosomes contain the remainder of a person’s genetic information. All human beings have 23 pairs of chromosomes by which genetic material is developed and characteristically demonstrated; 22 of these are autosomes, while the remaining pair (either XX, female, or XY, male) represents a person’s sex chromosomes. These 23 pairs of chromosomes work together to create the person we ultimately become. 37 Chromosomal abnormalities can occur during fetal development if something goes wrong during the replication of the cells. Common abnormalities include Down syndrome (caused by an extra chromosome #21), Klinefelter syndrome (caused by an extra X chromosome), and Turner syndrome (caused by a missing X chromosome). Genetic counseling is available for families to determine if any abnormalities exist that may be passed along to offspring. Many chromosomal abnormalities are of psychological importance, with substantial impacts on mental processes; for example, Down syndrome can cause mild to moderate intellectual disabilities. Genetic expression can be influenced by various social factors, as well as environmental factors, from light and temperature to exposure to chemicals. Our genetic destiny is not necessarily written in stone; it can be influenced by several factors, such as social factors, as well as environmental influences among which we live, including anything from light and temperature to exposure to chemicals. The environment in which a person is raised can trigger the expression of behavior for which a person is genetically predisposed, while the same person raised in a different environment may exhibit different behavior. Long-standing debates have taken place over the idea of which factor is more important, genes or environment. Is a person destined to have an outcome in life because of his or her genetic makeup, or can the environment (and the people in it) work to change what might be considered “bad” genes? Today, it is generally agreed upon that neither genes nor environment work alone; rather, the two works in tandem to create the people we ultimately become. Environmental elements like light and temperature have been shown to induce certain changes in genetic expression; additionally, exposure to drugs and chemicals can significantly affect how genes are expressed. People often inherit sensitivity to the effects of various environmental risk factors, and different individuals may be differently affected by exposure to the same environment in medically significant ways. For example, sunlight exposure has a much stronger influence on skin cancer risk in fair-skinned humans than in individuals with an inherited tendency for darker skin. The color of a person’s skin is largely genetic, but the influence of the environment will affect these genes in diverse ways. Gene-environment correlations, known as rage, can be explained in 3 ways—passive, evocative, or active. 2.6.1 The Influence of Genes on Behavior Genetic makeup has a significant role in determining human behavior. The influence of genes on behavior has been well established in the scientific community. To a considerable extent, who we are and how we behave is a result of our genetic makeup. While genes do not determine behavior, they play a huge role in what we do and why we do it. 2.6.2 Behavioral Genetics Behavioral genetics studies heritability of behavioral traits, and it overlaps with genetics, psychology, and ethology (the scientific study of human and animal behavior). Genetics plays a significant role in when and how learning, growing, and development occurs. For example, although environment influences the walking behavior of infants and toddlers, children are unable to walk at all before an age that is predetermined by their genome. However, while the 38 genetic makeup of a child determines the age range for when he or she will begin walking, environmental influences determine how early or late within that range the event will occur. 2.6.3 Classical Genetics Classical, or Mendelian, genetics examines how genes are passed from one generation to the next, as well as how the presence or absence of a gene can be determined via sexual reproduction. Gregor Mendel is known as the father of the field of genetics, and his work with plant hybridization (specifically pea plants) demonstrated that certain traits follow patterns. This is referred to as the law of Mendelian inheritance. Genes can be manipulated by selective breeding, which can have an enormous impact on behavior. For example, some dogs are bred specifically to be obedient, like golden retrievers; others are bred to be protective, like German shepherds. In another example, Seymour Benzer discovered he could breed certain fruit flies with others to create distinct behavioral characteristics and change their circadian rhythms. 2.6.4 The Influence of Behavior on Genes Behavior can influence genetic expression in humans and animals by activating or deactivating genes. Behavior can have an impact on genetic makeup, even as early as the prenatal period. It is important to understand the implications of behavior on genetic makeup to reduce negative environmental and behavioral influences on genes. EEG and PET scans can show psychologists how certain behaviors trigger reactions in the brain. This has led to the discovery of specific genes, such as those that influence addictive behaviors. A variety of behaviors have been shown to influence gene expression, including— but not limited to—drug use, exposure to the elements, and dietary habits. Drugs and Alcohol Prenatal exposure to certain substances, particularly drugs and alcohol, has detrimental effects on a growing fetus. The most profound consequences of prenatal drug or alcohol exposure involve newborn addiction and fetal alcohol syndrome (FAS). Fetal alcohol syndrome affects both physical and mental development, damaging neurons within the brain and often leading to cognitive impairment and below-average weight. Exposure to drugs and alcohol can also influence the genes of children and adults. Addiction is thought to have a genetic component, which may or may not be caused by a genetic mutation resulting from drug or alcohol use. Temperature Temperature exposure can affect gene expression. For example, in Himalayan rabbits, the genetic expressions of fur, skin, and eyes are regulated by temperature. In the warm areas of the rabbits’ bodies, the fur lacks pigment due to gene inactivity and turns white. On the extremities of the rabbits’ bodies (nose, ears and feet) the gene is activated and therefore pigmented (usually black). Himalayan rabbit: Exposure to cold temperatures activates pigment-producing genes in the rabbit’s extremities. Light Light exposure also influences genetic expression. Thomas Hunt Morgan performed an experiment in which he exposed some caterpillars to light and kept others in darkness. Those exposed to certain light frequencies had corresponding wing colors when they became 39 butterflies (for example, red produced vibrant wing color, whereas blue led to pale wings). Darkness resulted in the palest wing color, leading him to conclude that light exposure influenced the genes of the butterflies. In this manner a caterpillar’s behavior can directly affect gene expression; a caterpillar that actively seeks out light will appear different as a butterfly than one that avoids it. Nutrition Lack of proper nutrition in early childhood is yet another factor that can lead to the alteration of genetic makeup. Human children who lack proper nutrition in the first three years of life tend to have more genetic problems later in life, such as health issues and problems with school performance. 2.7 EUGENICS Eugenics, the selection of desired heritable characteristics to improve future generations, typically about humans. The term eugenics was coined in 1883 by British explorer and natural scientist Francis Galton, who, influenced by Charles Darwin’s theory of natural selection, advocated a system that would allow “the more suitable races or strains of blood a better chance of prevailing speedily over the less suitable.” Social Darwinism, the popular theory in the late 19th century that life for humans in society was ruled by “survival of the fittest,” helped advance eugenics into serious scientific study in the early 1900s. By World War I many scientific authorities and political leaders supported eugenics. However, it ultimately failed as a science in the 1930s and ’40s, when the assumptions of eugenicists became heavily criticized and the Nazis used eugenics to support the extermination of entire races. 2.7.1 Early History Although eugenics as understood today dates from the late 19th century, efforts to select mattings to secure offspring with desirable traits date from ancient times. Plato’s Republic (c. 378 BCE) depicts a society where efforts are undertaken to improve human beings through selective breeding. Later, Italian philosopher and poet Tommaso Campanella, in City of the Sun (1623), described a utopian community in which only the socially elite can procreate. Galton, in Hereditary Genius (1869), proposed that a system of arranged marriages between men of distinction and women of wealth would eventually produce a gifted race. In 1865 the basic laws of heredity were discovered by the father of modern genetics, Gregor Mendel. His experiments with peas demonstrated that each physical trait was the result of a combination of two units (now known as genes) and could be passed from one generation to another. However, his work was largely ignored until its rediscovery in 1900. This fundamental knowledge of heredity provided eugenicists—including Galton, who influenced his cousin Charles Darwin—with scientific evidence to support the improvement of humans through selective breeding. The advancement of eugenics was concurrent with an increasing appreciation of Darwin’s account for change or evolution within society—what contemporaries referred to as social Darwinism. Darwin had concluded his explanations of evolution by arguing that the greatest step humans could make in their own history would occur when they realized that they were not completely guided by instinct. Rather, humans, through selective reproduction, had the ability to control their own future evolution. A language pertaining to reproduction and eugenics developed, leading to terms such as positive eugenics, defined as promoting the proliferation of “good stock,” and negative eugenics, defined as prohibiting marriage and 40 breeding between “defective stock.” For eugenicists, nature was far more contributory than nurture in shaping humanity. During the early 1900s eugenics became a serious scientific study pursued by both biologists and social scientists. They sought to determine the extent to which human characteristics of social importance were inherited. Among their greatest concerns were the predictability of intelligence and certain deviant behaviour. Eugenics, however, was not confined to scientific laboratories and academic institutions. It began to pervade cultural thought around the globe, including the Scandinavian countries, most other European countries, North America, Latin America, Japan, China, and Russia. In the United States the eugenics movement began during the Progressive Era and remained active through 1940. It gained considerable support from leading scientific authorities such as zoologist Charles B. Davenport, plant geneticist Edward M. East, and geneticist and Nobel Prize laureate Hermann J. Muller. Political leaders in favor of eugenics included U.S. Pres. Theodore Roosevelt, Secretary of State Elihu Root, and Associate Justice of the Supreme Court John Marshall Harlan. Internationally, there were many individuals whose work supported eugenic aims, including British scientists J.B.S. Haldane and Julian Huxley and Russian scientists Nikolay K. Koltsov and Yury A. Filipchenko. 2.7.2 Eugenics Organizations and Legislation Galton had endowed a research fellowship in eugenics in 1904 and, in his will, provided funds for a chair of eugenics at University College, London. The fellowship and later the chair were occupied by Karl Pearson, a brilliant mathematician who helped to create the science of biometry, the statistical aspects of biology. Pearson was a controversial figure who believed that environment had little to do with the development of mental or emotional qualities. He felt that the high birth rate of the poor was a threat to civilization and that the “higher” races must supplant the “lower.” His views gave countenance to those who believed in racial and class superiority. Thus, Pearson shares the blame for the discredit later brought on eugenics. In the United States, the Eugenics Record Office (ERO) was opened at Cold Spring Harbor, Long Island, New York, in 1910 with financial support from the legacy of railroad magnate Edward Henry Harriman. Whereas ERO efforts were officially overseen by Charles B. Davenport, director of the Station for Experimental Study of Evolution (one of the biology research stations at Cold Spring Harbor), ERO activities were directly superintended by Harry H. Laughlin, a professor from Kirksville, Missouri. The ERO was organized around a series of missions. These missions included serving as the national repository and clearinghouse for eugenics information, compiling an index of traits in American families, training fieldworkers to gather data throughout the United States, supporting investigations into the inheritance patterns of human traits and diseases, advising on the eugenic fitness of proposed marriages, and communicating all eugenic findings through a series of publications. To accomplish these goals, further funding was secured from the Carnegie Institution of Washington, John D. Rockefeller, Jr., the Battle Creek Race Betterment Foundation, and the Human Betterment Foundation. Prior to the founding of the ERO, eugenics work in the United States was overseen by a standing committee of the American Breeder’s Association (eugenics section established in 1906), chaired by ichthyologist and Stanford University president David Starr Jordan. Research from around the globe was featured at three international congresses, held in 1912, 1921, and 1932. In addition, eugenics education was monitored in Britain by the English 41 Eugenics Society (founded by Galton in 1907 as the Eugenics Education Society) and in the United States by the American Eugenics Society. Following World War, I, the United States gained status as a world power. A concomitant fear arose that if the healthy stock of the American people became diluted with socially undesirable traits, the country’s political and economic strength would begin to crumble. The maintenance of world peace by fostering democracy, capitalism, and, at times, eugenics- based schemes was central to the activities of “the Internationalists,” a group of prominent American leaders in business, education, publishing, and government. One core member of this group, the New York lawyer Madison Grant, aroused considerable pro-eugenic interest through his best-selling book The Passing of the Great Race (1916). Beginning in 1920, a series of congressional hearings was held to identify problems that immigrants were causing the United States. As the country’s “eugenics expert,” Harry Laughlin provided tabulations showing that certain immigrants, particularly those from Italy, Greece, and Eastern Europe, were significantly overrepresented in American prisons and institutions for the “feebleminded.” Further data were construed to suggest that these groups were contributing too many genetically and socially inferior people. Laughlin’s classification of these individuals included the feebleminded, the insane, the criminalistic, the epileptic, the inebriate, the diseased—including those with tuberculosis, leprosy, and syphilis—the blind, the deaf, the deformed, the dependent, chronic recipients of charity, paupers, and “ne’er-do- wells.” Racial overtones also pervaded much of the British and American eugenics literature. In 1923 Laughlin was sent by the U.S. secretary of labour as an immigration agent to Europe to investigate the chief emigrant-exporting nations. Laughlin sought to determine the feasibility of a plan whereby every prospective immigrant would be interviewed before embarking to the United States. He provided testimony before Congress that ultimately led to a new immigration law in 1924 that severely restricted the annual immigration of individuals from countries previously claimed to have contributed excessively to the dilution of American “good stock.” Immigration control was but one method to control eugenically the reproductive stock of a country. Laughlin appeared at the centre of other U.S. efforts to provide eugenicists greater reproductive control over the nation. He approached state legislators with a model law to control the reproduction of institutionalized populations. By 1920, two years before the publication of Laughlin’s influential Eugenical Sterilization in the United States (1922), 3,200 individuals across the country were reported to have been involuntarily sterilized. That number tripled by 1929, and by 1938 more than 30,000 people were claimed to have met this fate. More than half of the states adopted Laughlin’s law, with California, Virginia, and Michigan leading the sterilization campaign. Laughlin’s efforts secured staunch judicial support in 1927. In the precedent-setting case of Buck v. Bell, Supreme Court Justice Oliver Wendell Holmes, Jr., upheld the Virginia statute and claimed, “It is better for all the world, if instead of waiting to execute degenerate offspring for crime, or to let them starve for their imbecility, society can prevent those who are manifestly unfit from continuing their kind.” 2.7.3 Popular Support for Eugenics During the 1930s eugenics gained considerable popular support across the United States. Hygiene courses in public schools and eugenics courses in colleges spread eugenic-minded values to many. A eugenics exhibit titled “Pedigree-Study in Man” was featured at the Chicago World’s Fair in 1933–34. Consistent with the fair’s “Century of Progress” theme, stations were organized around efforts to show how favourable traits in the human population could best be perpetuated. Contrasts were drawn between the emulative presidential 42 Roosevelt family and the degenerate “Ishmael” family (one of several pseudonymous family names used, the rationale for which was not given). By studying the passage of ancestral traits, fairgoers were urged to adopt the progressive view that responsible individuals should pursue marriage ever mindful of eugenics principles. Booths were set up at county and state fairs promoting “fitter families” contests, and medals were awarded to eugenically sound families. Drawing again upon long-standing eugenic practices in agriculture, popular eugenic advertisements claimed it was about time that humans received the same attention in the breeding of better babies that had been given to livestock and crops for centuries. 2.7.4 Anti-Eugenics Sentiment Anti-eugenics sentiment began to appear after 1910 and intensified during the 1930s. Most commonly it was based on religious grounds. For example, the 1930 papal encyclical Casti connubii condemned reproductive sterilization, though it did not specifically prohibit positive eugenic attempts to amplify the inheritance of beneficial traits. Many Protestant writings sought to reconcile age-old Christian warnings about the heritable sins of the father to pro- eugenic ideals. Indeed, most of the religion-based popular writings of the period supported positive means of improving the physical and moral makeup of humanity. In the early 1930s Nazi Germany adopted American measures to identify and selectively reduce the presence of those deemed to be “socially inferior” through involuntary sterilization. A rhetoric of positive eugenics in the building of a master race pervaded Rassenhygiene (racial hygiene) movements. When Germany extended its practices far beyond sterilization in efforts to eliminate the Jewish and other non-Aryan populations, the United States became increasingly concerned over its own support of eugenics. Many scientists, physicians, and political leaders began to denounce the work of the ERO publicly. After considerable reflection, the Carnegie Institution formally closed the ERO at the end of 1939. 2.8 GENETIC ENGINEERING Genetic engineering, the artificial manipulation, modification, and recombination of DNA or other nucleic acid molecules to modify an organism or population of organisms. Genetic engineering, sometimes called genetic modification, is the process of altering the DNA in an organism’s genome. This may mean changing one base pair? (A-T or C-G), deleting a whole region of DNA, or introducing an additional copy of a gene? It may also mean extracting DNA from another organism’s genome and combining it with the DNA of that individual. Genetic engineering is used by scientists to enhance or modify the characteristics of an individual organism. Genetic engineering can be applied to any organism, from a virus? to a sheep. For example, genetic engineering can be used to produce plants that have a higher nutritional value or can tolerate exposure to herbicides. 2.8.1 Historical Developments The term genetic engineering initially referred to various techniques used for the modification or manipulation of organisms through the processes of heredity and reproduction. As such, the term embraced both artificial selection and all the interventions of biomedical techniques, among them artificial insemination, in vitro fertilization (e.g., “test-tube” babies), cloning, and gene manipulation. In the latter part of the 20th century, however, the term came to refer more specifically to methods of recombinant DNA technology (or gene cloning), in which DNA molecules from two or more sources are combined either within cells or in vitro and are then inserted into host organisms in which they can propagate. 43 The possibility for recombinant DNA technology emerged with the discovery of restriction enzymes in 1968 by Swiss microbiologist Werner Arber. The following year American microbiologist Hamilton O. Smith purified so-called type II restriction enzymes, which were found to be essential to genetic engineering for their ability to cleave a specific site within the DNA (as opposed to type I restriction enzymes, which cleave DNA at random sites). Drawing on Smith’s work, American molecular biologist Daniel Nathans helped advance the technique of DNA recombination in 1970–71 and demonstrated that type II enzymes could be useful in genetic studies. Genetic engineering based on recombination was pioneered in 1973 by American biochemists Stanley N. Cohen and Herbert W. Boyer, who were among the first to cut DNA into fragments, rejoin different fragments, and insert the new genes into E. coli bacteria, which then reproduced. 2.8.2 Process and Techniques Most recombinant DNA technology involves the insertion of foreign genes into the plasmids of common laboratory strains of bacteria. Plasmids are small rings of DNA; they are not part of the bacterium’s chromosome (the main repository of the organism’s genetic information). Nonetheless, they can direct protein synthesis, and, like chromosomal DNA, they are reproduced and passed on to the bacterium’s progeny. Thus, by incorporating foreign DNA (for example, a mammalian gene) into a bacterium, researchers can obtain an almost limitless number of copies of the inserted gene. Furthermore, if the inserted gene is operative (i.e., if it directs protein synthesis), the modified bacterium will produce the protein specified by the foreign DNA. A subsequent generation of genetic engineering techniques that emerged in the early 21st century centred on gene editing. Gene editing, based on a technology known as CRISPR- Cas9, allows researchers to customize a living organism’s genetic sequence by making very specific changes to its DNA. Gene editing has a wide array of applications, being used for the genetic modification of crop plants and livestock and of laboratory model organisms (e.g., mice). The correction of genetic errors associated with disease in animals suggests that gene editing has potential applications in gene therapy for humans. Applications Genetic engineering has advanced the understanding of many theoretical and practical aspects of gene function and organization. Through recombinant DNA techniques, bacteria have been created that are capable of synthesizing human insulin, human growth hormone, alpha interferon, a hepatitis B vaccine, and other medically useful substances. Plants may be genetically adjusted to enable them to fix nitrogen, and genetic diseases can possibly be corrected by replacing dysfunctional genes with normally functioning genes. Nevertheless, special concern has been focused on such achievements for fear that they might result in the introduction of unfavourable and possibly dangerous traits into microorganisms that were previously free of them—e.g., resistance to antibiotics, production of toxins, or a tendency to cause disease. Likewise, the application of gene editing in humans has raised ethical concerns, particularly regarding its potential use to alter traits such as intelligence and beauty. 2.8.3 Controversy In 1980 the “new” microorganisms created by recombinant DNA research were deemed patentable, and in 1986 the U.S. Department of Agriculture approved the sale of the first living genetically altered organism—a virus, used as a pseudorabies vaccine, from which a single gene had been cut. Since then several hundred patents have been awarded for 44 genetically altered bacteria and plants. Patents on genetically engineered and genetically modified organisms, particularly crops and other foods, however, were a contentious issue, and they remained so into the first part of the 21st century. 2.9 SUMMARY Behavioural genetics is the interdisciplinary effort to establish causal links between genes and animal (including human) behavioural traits and neural mechanisms. Methods used include twin studies, quantitative trait mapping by linkage to allelic variants, transgenic animals and targeted gene disruption or silencing. Behavioral genetics is the study of genetic and environmental influences on behaviors. By examining genetic influence, more information can be gleaned about how the environment operates to affect behavior. Almost all behaviors studied by psychologists are affected by our genetic makeup, and so the question is not whether genes are important, but how do they affect these behaviors? The old nature–nurture debate has been laid to rest by students of this discipline. We know, from thousands of studies using many different methodologies, that both genes and environment are important to understand if we hope to untangle the mysteries of virtually any behavior. Among the interesting questions to be asked now: How do genes and environments work together to influence behaviors, and what specific genes might be responsible for distinct types of behaviors and what is their mechanism of action? Human behavioral genetic research aimed at characterizing the existence and nature of genetic and environmental influences on individual differences in cognitive ability, personality and interests, and psychopathology is reviewed. Twin and adoption studies indicate that most behavioral characteristics are heritable. Nonetheless, efforts to identify the genes influencing behavior have produced a limited number of confirmed linkages or associations. Behavioral genetic research also documents the importance of environmental factors, but contrary to the expectations of many behavioral scientists, the relevant environmental factors appear to be those that are not shared by reared together relatives. The observation of genotype-environment correlational processes and the hypothesized existence of genotype-environment interaction effects serve to distinguish behavioral traits from the medical and physiological phenotypes studied by human geneticists. Behavioral genetic research supports the heritability, not the genetic determination, of behavior 2.10 QUESTIONS 1. What do you mean by Behaviour Genetics? 2. What is nature and scope of behaviour genetics? 3. Write a brief note on history of behaviour genetics? 4. Explain the relationship between genetics and eugenics. 5. Write a note on research methods in behaviour genetics. 6. Briefly discuss on Twin Studies. 45