behavioural genetics: the study of the genetic and environmental contributions to individual differences in personality and behavior.

Transcription

1 Chapter 6 Genetics. - the researchers looked for genetics and environmental differences between the youths who were depressed and those who were not. The amazing thing is that they found- nothing! - They found no impact of either genes or environment can rates of depression. genotype: the genetic makeup that codes for a specific trait Both genes and environment affect our personalities behavioural genetics: the study of the genetic and environmental contributions to individual differences in personality and behavior. behavior genetics answers question how do genes and environment work together to make us the kind of people we are. Nature and Nurture as Allies -the best characterization of nature-nurture issue is that nature and nurture transact. That is, genes and environment can work separately, together or they may influence one another genotype-environment interaction: combination of nature and nurturance -yet, another possibility is that it may be impossible to separate the effects of genes from the effects of the environment. genotype-environment correlation: when a genotype is exposed differently to an environment; when personality affects the environment people find themselves in. genotype- environment correlations may be passive, reactive or active. When we cannot separate the affect or impact of genes from the environment. phenotype: the manifestation of the genes; the observable physical or psychological trait which is coded by the genes. phenotype= genotype + environment+ gene environment correlation + gene environment interaction Genes and Environment as Co-actors Heritability Heritablility (h2) is the amount of observed individual differences in same characteristics that can be accounted for genetic differences.

2 heritability refers to differences across a group or population of people, not to a specific person. with heritability, we cannot know what contributes more to the personality of a particular person, but we can know how much genetics and environment each account ofr differences in a particular personality characteristic of this particular sample of people. heritability refers to the inheritance of a particular trait in a particular population at a particular time, so sometimes heritability estimates differ depending on the exact sample and methods used by researchers. Enviromentality environmentality (e2) estimates the extent ot which observed individual differences can be traced in any way to individual differences in environment. - together, heritability, environmentality and measurement error accounts for the differnces we see among people on a given characteristic. - the greater the heritability of a characteristic the less the environmentality. And the greater the environmentality, the less the heritability. Shared and Non-shared environment environment referred only to any part of the phenotype not accounted for by genes, however, these days researchers are trying to zero in on and specifically identify the exact aspects of an environment that account for differences in personality among a group of people. shared environment includes aspects of the family environment that are generally same for all children in a household, including physical, psychological and social aspects. physical aspects - the type of dwelling (eg. apartment vs house and its layout) - the number of books/computers at home - the presence of a video game system psychological aspects - eg. home atmosephere, parenting practices, the quality of sibling interactiosn, psychopathology( alcoholism, drug use, depression) in home. social variables - eg. socioeconomic status, family structure, education attainment of parents, an urban or rural setting and religion. non-shared environment includes experiences that relatives have which makes hem different from one another. -this may include: unique experiences within the family ( being the eldest child, being the only boy, spacing of siblings, differential parental treatments.) outside the family (peers, teachers, sports, hobbies)

3 -when it comes to personality, most of the environmental influence ends up being of the non-shared variety. - when family members resemble one another it is more due to the heredity than to shared environment. That is, children growing up in the same family are not any more similar than children growing up in different families. - certainly environment is important; however, the important aspects of the environment for personality development do not appear to be shared by family members - it may be that family environment takes children different from one another, or it may be that researchers are looking tooo broadly and have not identified specific aspects of the environment that are shared. -also parents may handle children differently depending on their personality, creating a unique environment for each child. Estimating Heritability we estimate that heritability of a characteristic by seeing if people who have similar genes show similar characteristics. -if the characteristic has a strong genetic component then we would expect identical twins who hare 100% of their genes to be more similar than strangers in that charcteristics. We can see this more clearly in physical characteristics, but it is harder to see the effects of genes and environment in personality. monozygotic (MZ) twins: identical twins who have exact genetic duplicates of each other. This happens when a fertilized egg, the zygote, split into two (or sometimes more) identical parts that each go on to develop a fetus; they share 100% common genetic makeup. dizygotic (DZ) twins: fraternal twins occur when two zygotes develop in utero at the same time. DZ twins result from the fertilization of the different eggs by wo different sperm cells, hence they are genetically distinct. - essentially fraternal twins are no more alike than ordinary siblings, sharing about 50% of their genes. - although twins may look alike, the only way to be sure if they are identical (MZ) or fraternal (DZ) is to conduct a gentic test (of course, if the twins are of different sexes, then we should know that they must be fraternal twins). h2 = 2 (rmz - rdz )

4 - a second way of estimating heritability is to compare identical twins who have been raised in separate environments - called MZA twins ( monozygotic twins raised apart) -if such twins score similarly in a trait such as extroversion, then we know extroversion has a strong genetic component. h2= rmza - second formula for estimating heritability equal environment assumption applies only to similar treatment (environmental affects) that is related to the specific characteristic under study. Twins equal environment, equal things but it might get them differnet personality the assumption that identical twins are not treated more alike than fraternal twins, an assumption behind the double-the-difference between MZ and DZ twins reared apart measuere of heritability. assumption of reprentiveness: the assumption that identical twins are typical of the population on the specific characteristic under investigation, an assumption behind double-the-difference between MZ and DZ twins reared about measure of heritability. Many people can be apply to population you generale that results to everyone, twin are different with siblings the issue of common low birth weight/ prematurity of twins- problematic of reprentativeness. -rmza method of estimating heritability also has its limitations researchers assume that adopted families of each twin are different from each other; twins may be more alike on a certain characteristic due to selective placement during the adoption process and not their genetics. (selective placement: the assumption that adopted families of MZ twins raised apart are different fro each toher, that the identical twins were not purposely placed in similar environments, an assumption behind the rmza measure of personality; selective placement makes it impossible to see the effect of genetics apart from the effect of environment because it confounds the two). adoption studies of MZA twins also assume that families who adopt are the same as families who do not adopt. Selective placement- twins raised apart are different from each other Heritability of Common Personality Characteristics A solid finding in the research one that has been well replicated across many samples and for both self-report and other report is that virtually all individual differences in human behavior

5 including cognitive abilities, personality, social attitudes, psychological interests, and psychopathology are moderately heritable. The heritability of personality traits ranges from.40 to.60 and is the same for both men and women. Shared environment typically accounts for very little variation, whereas non-shared environment accounts for a great deal. The variance in personality traits typically breaks down like this: Observed differences in personality traits= 40% Genetics + 0% Shared Environment + 40% Non-shared environment + 20% Error So even after we account for the 40 to 60% of variation in most personality traits that come from genetics, there is still plenty of variance left to be explained. According to FFM model, human personality can be described using five broad categories of traits: neuroticism, extraversion, openness, agreeableness, and conscientiousness. Identical twins are very similar in the five factor traits, even if they are raised apart, indicating a moderately strong genetic component to these traits. Indeed, the heritability of all five factors is in the.41 to.50 range, indicating that about 41 to 50% of the variation in these traits is due to genetic factors. But identical twins that were raised together have the highest correlations and indeed, even fraternal twins who are raised together look a bit like each other even though fraternal twins share only about 50% of their genes on average. This suggests that there is a moderate effect of the environment too. The environment- both shared and nonshared- accounts for about 47 to 53% of the variance in these traits. The shared environment accounts for only about 8 to 17% of the variation in these traits. Other researchers have found similar results when looking at the individual facet traits that make up each of the five factors. Although each of the five factors have moderate heritability genetics accounted for about 35 to 60% of the variance in self-reported traits there was a great effect of nonshared environment on these traits. In fact, shared environment accounted for the smallest amount of variance in both self-reports and peer reports. Then and Now: The Science of Genetics -Johann Mendel ( ) : the person who started the whole field of genetics; the founder of modern genetics. -He studied the variation in plants and noticed that sometimes characteristics of plants seemed to skip a generation. He meticulously planted and recorded details of his pea plants and counted their offspring instead of merely generalizing the results as earlier researchers have done. - First, each parent plant passes on one form of the gene (Mendel used the word element) for a given characteristic to its offspring, who get two forms of the gene, one from each parent.

6 -allele: alternative forms of the same gene which occur in pairs, one inherited from each birth parent. - these two alleles can either be the same or different. When the alleles are different, one characteristic will be dominant over the other. However, both alleles will be passed on to the next generation. For example, say a pea plant with wrinkled peas breeds with a plant that has smooth peas. The next generation will each get some combination of alleles for smooth and wrinkly peas. If smoothness is the dominant characteristic, then the peas will look smooth, but the plants will still carry and pass on the recessive wrinkly pea trait to the next generation. This concept of dominance explains the pattern of seeds Mendel observed in successive generations. In fact, such inheritance pattern where one trait dominates over another is called Mendalian inheritance. Mendel s experiments with peas. About 99.9% of the human DNA sequence is the same for each and every one of us, it s that.1% that does differ that makes us unique individuals. Epigenetics: the study of how the environment changes the function of genes without changing the genes themselves. o EX: - when we come from India our genes are different, this environment effects our genes, its not changing our genes but it has an impact Gene: a sequence of DNA that codes for a specific trait; genes are composed of coding regions called exons (that part of a gene which codes for a specific trait) and noncoding regions called introns (that part of the gene which does not code for a specific trait but may orchestrate the functioning of nearby genes in direct response to the environment). The ends of allies introns ( they get cut off) ( JUNK)

7 The middle part of allie exons ( they always stay in the middle ) Of the 3.3 billion base pairs of DNA in the human genome, only about 2 to 3% are functioning genes. The remainder of the DNA- nearly 2 meters of it- was once thought to do nothing because it occurs outside genes. This so-called junk DNA is actually turning out to be more interesting than the coding genes themselves. Some of this junk appears to orchestrate- alter its regulation to underexpress or overexpress a nearby gene. In fact, some of these noncoding sequences end up changing how the genes function in direct response to the environment. A study by Cole et al indicates that significantly more genes that regulate immune functioning were turned down (not expressed at the same level) in the lonely group than in the socially supported group. Specifically, those cells that protect against disease were turned down (red), whereas genes that increased disease were turned up (green). These results suggest that loneliness directly impacts immune functioning by regulating the specific genes that control immune functioning. Positional cloning: a possible way of preventing inherited diseases by replacing defective genetic code with corrected code that matches the gene as closely as possible. Replaying a allie with another allie, which is not detective, an d the codes are very similar Gene and Environment: A Dialectical Synthesis When it comes to personality, often gens and environment influence each other. According to the philosopher Hegel, dialectic is a way of thinking in which contradictions are seen to be part of a higher truth. For example, the nature-nurture debate suggests that nature and nurture work in opposition. Until the 1980s, researchers had been considering genes and environment only as separate factors influencing phenotype. Plomin et al (1977) suggested that researchers can increase the accuracy of their results- and detect new effects- by specifically testing for two ways in which genes and environment influence each other: a genotype-environment interaction and a genotype-environment correlation. A genotype-environment interaction occurs when a genotype is responds differently to an environment; a genotype-environment correlation occurs when a genotype is exposed differently to an environment. We can explore only genotype-environment interactions and genotype-environment correlations within a population but not in a single individual. Secondly Plomin et al noted that in practice it is sometimes difficult to distinguish genotypeenvironment interactions from genotype-environment correlation. Genotype-Environment Interactions

8 Genotype-environment interaction is when people respond differently to the same environment because of their differing genetic makeup. That is, the environment has a different impact depending on a person s genotype. In a sample of juvenile delinquents in Russia even though many of the boys experienced maternal rejection in their lives (e.g. physical punishments, lack of respect for their pint of view, public criticism), only those with a certain genotype experienced clinical depression. This is an example of genotype-environment interaction. The same environment- maternal rejection- led to clinical depression only in boys with one specific genotype. Maternal rejection was not correlated with clinical depression, so these really are separate effects. The gene (DATI or SLC6A3) is one of the three variations of a gene suspected to be related to depression. This gene is an important regulator of the neurotransmitter dopamine. Evidence suggests that prolonged exposure to dopamine may lead to depression. Despite knowing which genes are related to dopamine functioning, scientists have been unable to rpve that these gens cause depression. No genetic difference has been found between depressed and nondeoressed people. Shared environments may impact the personality trait of Neuroticism through genotypeenvironment interactions. By not considering interactive effects of environment on genes, researchers may have accidentally overestimated genetic effects and underestimated the impact of shared environments. A second potential genetic risk factor for depression, anxiety and other mood disorders involves a certain region of the serotonin transporter gene. People actually get two versions of the gene that regulates serotonin one from each parent. This leads to three different variations of the gene depending on which allele a person gets from his or her parents: ss, sl, and ll. These letters stand for the short (s) and long (l) versions of the gene. People with the short version (sl or ss), especially two short alleles (ss) are less efficient at regulating serotonin so they are at risk for depression, whereas people with two long allele (ll) may have a measure of protection from depression. There were no differences in number of life stressors among the three genotype groups suggesting that genes did not cause people to experience more life stressors. One group of researchers suggested that such interactions probably occur more often than we realize, especially for psychopathology. Interactions between genes and environment have been found to account for religious upbringing lessening the impulsiveness of high sensation seekers, parental bonding and family functioning decreasing emotion instability, a monoamine oxidase A (MAOA) promoter gene and parental harshness increasing adolescent antisocial behavior, the DRD2 gene and stress increasing alcoholism and negative life events increasing Neuroticism. Genotype-Environment Correlations Measures of environments showed evidence of genetic influence. In other words, measures of environmental effects such as parenting styles on, or peer ratings of, a child, for example, were not strictly environmental.

9 People s personalities affected the environments they found themselves in and also how they described these environments on questionnaires. People construct teir environments. We select, modify, create, and re-create in our memory ( and on questionnaire administered by researchers) our experiences. When people s experiences are related to- that is, are correlated with their genetic inclinations we call this a genotype-environment correlation. A genotype-environment correlation occurs when people with a gene for a specific characteristic find themselves in an environment that fosters- or discourages- the expression of that characteristic. People with different genotypes are exposed to different environments depending on that genotype. Because both the genes and the environment occur together, we can t be sure which is causing the manifestation of the characteristic. A genotype-environment correlation occurs when people with high genetic value (i.e., a strong genetic predisposition for a specific characteristic) find themselves in environments with high values (i.e., environments that push for that characteristics). Similarly, a genotype-environment correlation also occurs when people with low genetic values (i.e., no particular inclination for a characteristic) find themselves in environments with low values (i.e., environments with no particular demand for that characteristic). Three types of Genotype- Environment Correlations TYPE DESCRIPTION PERTINENT ENVIRONMENT Passive Children are given genotypes linked to their Natural parents and siblings environment Reactive Children are reacted to on the basis of their Anybody genotype Active Children seek an environment conductive to their genotype. Anytime Passive genotype-environment correlation: when a genotype is exposed to an environment but has done nothing to obtain the environment.(when parents provide both the genes and an environment that is favorable (or unfavorable) to the development of those genes). - The environment is the child s immediate environment: parents, siblings, and other members of the household that he or she is born into. - For example, parents who have very high verbal skills- gifted even- who not only pass on these fabulous genes to their children but also provide a home filled with books and games and other activities that are likely to help their children develop good verbal skills.

10 - Because the children did nothing to cause the environment to provide these resources- and in fact, such resources may have been in place long before children were even on the scene- the genotype-environment correlation is passive. Reactive genotype-environment correlation: when the environment responds to certain personalities because of their genotype. - The environment is any person who interacts with or responds to the child. - For example, highly verbal parents who see that their baby is babbling constantly and often seems as if she is trying to communicate to them. These parents may purposely try to engage the bay in conversation or encourage the baby to talk. Because the parents are responding to something in the child, it s called reactive genotype-environment correlation. - With both reactive genotype-environment correlation and passive genotype-environment correlation, we can t be sure if the child s genetics or environment caused him or her to be so verbal because the two co-occurs. Active genotype-environment correlation: when people with a certain genotype seek out a specific environment because of their personality. - The environment can be other people or indeed, the physical environment. - For example, imagine a child of highly verbal parents is spending the weekend with grandparents (with who the child shares about 25% of her genes, on average). Suppose the baby babbles to both grandparents, but because Grandma is in the middle of cooking dinner, Grandpa investigates the noises coming from the crib. For the rest of the weekend, the baby crawls to Grandpa wherever he is and continues to babble at him. This would be an example of an active genotype-environment correlation. Here, the parents have provided both with genes and the environment. The baby can either interact with Grandma or Grandpa, but she chooses to talk with, and indeed seeks out, the more responsive one, Grandpa. Here, her high verbal ability comes from both her genetic and the environment, but she is the one who specifically seeks out the environment. - Genotype-environment correlations can be either positive or negative. Positive genotype-environment correlations: where the conditions were favourable for developing a certain characteristic. In this case, verbal behavior was encouraged in the child either by an environment that just happens to encourage verbal ability (passive), responded to the child (reactive), or which the child sought out (active). Negative genotype-environment correlation: when a genotype is exposed differently to an environment that is unfavourable for developing certain characteristics. For example, and environment may discourage the development of certain personal characteristics. - People with high genetic values for a characteristic find themselves in environments with low values for that characteristic. Often the result is that the environment discourages the expression of that characteristic. - The inverse is possible, where people with low genetic values for a characteristic find themselves in environments with high values for that characteristic. They may end up developing some of their less pronounced characteristics

11 - Whether a genotype-environment correlation is positive or negative does not depend on the ultimate outcome that development or lack of development of a characteristic- but on the relative levels of the genotype and the environment. Positive and Negative Genotype-Environment Correlations TYPE OF CORRELATION GENOTYPE ENVIRONMENT Positive High High Positive Low Low Negative High Low Negative Low High (High or Low indicates the amount of the characteristic present in the gens or in the environment) - For personality characteristics, Raymond Cattel suggested that negative genotype-environment correlations were probably more common than positive correlations. - The relative importance of these environments and hence the type of genotype-environment correlation that is operating-shift over the life span. For example, passive genotypeenvironment influences may decrease from infancy to adolescence whereas active genotypeenvironment influences increase as the child experiences more of the world away from home. What s the Evidence? Researching Genotype-Environment Correlations. - One way to find a reactive genotype-environment correlation is to look at twin studies over time, where we might be able to see changes in a child s behavior and if these changes correlate with changes in the environment. - For example, comparing MZ twins and DZ twins, Narustye et al. found that childhood aggression was related to parental criticism that was related, in turn, to self-reported antisocial behavior in adolescents. - The researchers suggested that this is an example of a reactive genotype-environment correlation: Children at risk for antisocial behavior are indeed more aggressive than children not at risk, and they are also more likely to elicit negative reactions in their parents. - In positive reactive genotype-environment correlation, genes cause behavior to which the environment, in this case other people, then responds. - There are many examples of gene-environment correlations, especially in development psychology. Correlations between genes and environment have been found for adolescents perceptions of parental warmth or conflict, physical punishment, and misbehavior, parental harshness and antisocial behaviors, memories of childhood environment and family bonding and neuroticism.