genetics and behaviour Flashcards
definition of genetic inheritance
biological transmission of characteristics from one generation to the next. we inherit genes from our parents. these genes influence physiological processes and these tend to guide behavior. human behavior is often the result of complex interaction between genes, physiological processes and environment.
what is a gene?
a gene is the basic physical and functional unit of heredity. each chromosome is composed of many individual heredity units called genes. a gene is a segment of deoxyribonucleic acid (DNA).
alleles are different forms of the gene.
genetic research assumptions and methods
assumptions:
-genotype and phenotype, family genetic relatedness and evaluation
methods:
-family/twin resemblance correlations, adoption studies, selective breeding studies and molecular genetics.
do genes determine behavior?
no, genes do not determine behavior. it is likely that genes could contribute to behavior but it is unlikely that they determine behavior.
what is the most serious limitation of family study
is that the influence of genetic cannot be separated from the influence of environmental factors.
passive, evocative, and active interactions.
passive interaction:
-if genes contribute to a certain trait in a child, say aggressiveness, it is likely that those genes and the trait are also present in one parent. aggressiveness will therefore be common in the child’s environment. it is therefore impossible to tell whether and to what extent the child’s aggressiveness is a result of genetic or environmental factors.
evocative interaction:
-in case a child has inherited genes that contribute to aggressiveness in the child, the child may express aggressiveness. this kind of behavior may evoke aggressiveness in the child’s environment and thereby further strengthen the aggressiveness of the child.
active interaction:
-an inherited behavioral tendency makes the individual create or search for environments where the trait can be freely expressed and thereby strengthened. an aggressive child may for instance prefer conditions that he/she finds rewarding, and therefore seek peers that are aggressive.
studies to find out what genes are responsible for our behavior
one method is the use of gene knockout mice:one way used to identify the function of a particular gene is to genetically manipulate mice because men and mice have many genes in common. the gene that the researchers want to understand is replaced or disrupted with an artificial piece of DNA. another is linkage studies.
study 1 (genes and behavior)
Rushton et al (1986). Altruism and aggression: the heritability of individual differences.
aim: to examine the genetic influence on individual differences in altruism and aggression.
pps: 573 adult twin pairs of both sexes. (approx. 1400 were mailed the questionnaires). identical and fraternal twins raised together; age 19-over 60.
procedure: 5 questionnaires measuring altruism, empathy, nurturance, aggressiveness, and assertiveness. correlations were calculated for each trait.
results: correlations were 53,54,49,40,52 for monozygotic pairs and 25,20,14,04,20 for same sex dizygotic pairs. heritability estimates 56%, 68%, 70%, 72% and 64%. age and gender differences were found as well. women had higher scores than men on altruism and lower scores on aggressiveness. altruism increased over the age span 19-60 and aggressiveness decreased.
conclusion: there is genetic contribution to altruism, empathy, nurturance, aggressiveness, and assertiveness. the study clearly indicates that the genetic basis of behavior needs to be taken into consideration if a full understanding of human personality is to be achieved.
study 2 (genes and behavior)
Caspi et al (2003) influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene.
aim: to investigate whether the short allelein the 5HTT gene in combination with stressful life events increases the risk of depression in an individual (to determine whether there is evidence for a gene-environmental interaction for a mutation of the serotonin transporter gene- 5HTT)
pps: 847 new zeland caucasian non-maori 26-year-olds.
procedure: pps were genotyped and divided into three groups based on their 5HTT alleles: group 1 had two shorts allele; group two had one short one long; group 3 had two long. the mutation of the 5HTT gene has the shorter alleles. roughly 43% of people have the shorter alleles. a “stressful life events” questionnaire which askedthem abt the frequency of 14 different events- including finance, employment, health and relationship stressors- between the ages of 21 and 26. they were also assessed for depression.
results: pps who had inherited one ormore short versions of the allele demonstrated more symptoms of depression and suicidal ideation in response to stressful life events. the effect was strongest for those with three or more stressful life events. simply inheriting the gene wasn’t enough to lead to depression, but the genes’ interaction with stressful life events increased one’s likelihood of developing depression.
study 3( evolutionary)
Clark and Hatfield (1989) Gender differences in receptivity to sexual offers.
aim: to investigate the differences in choosiness shown by males and females when approached by a stranger offering sex ( to test whether men are more open to casual sex than are women)
pps: 48 males and 48 females undergraduate students (18-22) at Florida State University. an opportunity sample.
procedure: pps were approached by an average attractive person of the opposite sex (5 female and 4 male confederated were used, approx 22 years old) asking one of the three following questions: “I’ve watched you around campus, I find you very attractive”… 1)”would you fo out with me tonight?” 2)”would you come over to my apartment tonight?” 3)”would you go to bed with me tonight?” the confederates were instructed to only approach pps whom they found genuinely attractive and with whom they would actually consider having sex. the DV was whether the pps answered “yes” or “no”.
results: men accepted the apartment-request and the bed request much more often than did women. in many cases when men did not accept, they gave excuses such as “I am married” while women never gave excuses. instead they said “you’ve got to be kidding, leave me alone.” the request for a date was met with around 50% agreement from both men and women.
conclusion: it seems that men are more eager for sex with strangers than are women. women do appear to operate a system of increased choosiness when it comes to their sexual behavior, whereas men seem to be less bothered by a possibly risky sexual encounter with a stranger. that supports the evolution theory of mate selection.
study 4 (evolutionary)
Wedekind (1995) MHC-dependent mate preferences in humans
aim: will women be able to smell the difference between the similar and dissimilar MHC of different men, and will this difference affect the attraction women feel for these men?
pps: 49 female students and 44 male students (they didn’t know each other) were examined to establish their MHC types. because pill-contraceptives in women simulate pregnancy, and therefore could confound the results, women were also asked to report whether or not they took any oral contraceptives.
procedure: the men were provided with a clean new 100% cotton t-shirt and asked to wear it for two night and keep it in an open plastic bag when not wearing it. they were also to stay away from any foods and activities involving smells (cheeses, tobacco, sex) and to sleep alone in their beds. they were given odor-free cleaning material and deodorants for this duration.
starting the day after, the women were asked to rate the smell of seven t-shirts each: 3 of which had been worn by men with similar MHC and three by men with dissimilar MHC + one control. the women scored the t-shirt smell on pleasantness (scale 0-10, t is natural). whenever possible, the testing was timed to the second week of the woman’s menstrual cycle because that is the time that women are most smell-sensitive. each woman was also giving a copy of Suskind’s novel Perfume to sensitize their smell perception.
results: women who were not taking the pill preferred the smell of men with dissimilar MHC. However, this result was reversed for women who were taking the pill.
conclusion: these results provide evidence that sexual selection in humans is partly based on selecting partners with dissimilar MHC. however, the artificial nature and limited scope of this study does not allow for generalization to all groups or situations. it does raise preliminary concern that oral contraceptives may have side-effects which are not well-understood or known among prescribers.
discussion: the study has been successfully replicated.
what is the Major Histocompatibility Complex (MHC)?
while several theories abound there is also the possibility that sexual selection lets animals identify the individual partners with which they are more likely to have healthy offspring. one factor known to be important for health is the MHC, which is a large group of genes responsible for the development of the immune system. different genes in the MHC affect vulnerability to different infections, thus protecting the carrier against diseases. it makes evolutionary sense that individuals select partners with as little similarity in MHC as possible, thereby giving the offspring the greatest MHC diversity, and therefore widest protection against disease. it had already been demonstrated that mice will choose, by smell, the sexual partner which has the most dissimilar MHC, and the challenge now was to show this effect in humans as well.
what is the diathesis-stress theory?
look at the handout.
