Chapter 6: Genetics and Personality Flashcards
what is a genome
- the complete set of genes an organism possesses –> has 20000-30000 genes each
- the nucleus of each cell in the body contains two complete sets of the human genome (one from mother one from father) except for egg/sperm/red blood cells
what are two noteworthy findings of the human genome project
- the manner in which human genes get decoded into proteins is far more variable than in other species, which gives more variety in proteins
- “junk DNA” have large impacts, not only protein-coding genes
what is genetic junk
- 98% of DNA in human chromosomes that aren’t protein-coding genes –> not actually “junk”, have huge impacts
- now referred to as pseudogenes and riboswitches
describe differences and similarities between human genomes
- most of the genes in the genome are the same for everyone in the planet –> thus we all have two legs, 10 fingers, etc.
- small number of genes are different –> code for different eye colours, etc.
describe the field of behavioural genetics
- attempts to determine the degree to which individual differences in personality are caused by genetic and environmental differences
- gain popularity e.g. “why some people are born to travel”
why is the field of behavioural genetics controversial
- people worry that findings will be misused to support political agendas (e.g. if genes are the cause of behaviours, should we not hold people accountable?)
- worry that this will invalidate the possibility for change
- support for Eugenics –> creating a master race
what is Eugenics
notion that we can design the future of the human species by fostering reproduction of people with certain traits and discouraging the reproduction of people without these traits –> creation of a “master race”
why do people argue for the study of behavioural genetics
- genetic findings need not lead to Eugenics
- Knowledge is better than ignorance
what are the primary goals of behavioural genetics
- determine the percentage of individual differences that can be attributed to genetic/environmental differences –> “percentage of variance”
- determine ways genes and environment interact and correlate with each other
describe the genetic/environmental influences on height
genetics accounts for 90%, and environment (e.g. diet) accounts for 10%
what is percentage of variance
individuals vary and this variability can be partitioned into percentages that are due to different causes
what is heritability
- statistic referring to the proportion of observed variance in a group of individuals that can be accounted for by genetic variance
- degree to which genetic differences among individuals cause differences in an observed property
describe the two components of the definition of heritability
- proportion of phenotypical variance that is attributable to genotypic variance
- phenotypic variance = observed individual differences (e.g. height)
- genotypic variance = individual differences in total collection of genes possessed by each person
what does a heritability of .50 mean?
- 50% of the observed phenotypic variation is attributable to genotypic variation
- environmental component is proportion of phenotypic variance NOT attributable to genetic variance, thus the environmental component is .50 too
- NOTE: assumes no correlation/interaction between environment and genes
what is environmentality
percentage of observed variance in a group of individuals that can be attributed to environmental (nongenetic) differences
what are the three misconceptions about heritability
- it can be applied to a single individual –> only on group level
- it is constant –> statistic applies to a population at one point of time, and depends on the population
- it is a precise statistic –> error and unreliability is always likely, just an estimate
what is the nature-nurture debate at the level of the individual
- there is no nature-nurture debate
- everyone has a unique set of genes and environmental circumstances
- inseparable intertwining of nature and nurture on the individual level
- e.g. what is most important part of a cake –> doesn’t make sense to ask this
what is the nature-nurture debate at the level of the population
- we can disentangle the influence of genes and environment
- level of analysis where behavioural geneticists operate
- can ask what is more important for accounting for differences in a given trait in the population
- e.g. sweetness causes differences in the taste of cakes as a population
what are the four methods of behavioural genetics
- selective breeding with animals
- family studies
- twin studies
- adoption studies
describe the behavioural genetics method of selective breeding
- identifying dogs that possess the desired characteristic and having them mate only with other dogs that also possess this same characteristic
- this is why dog breeders are successful –> qualities are moderately to highly heritable (mostly physical traits, but also behavioural traits like aggression)
what has selective breeding taught us about heritability
heritability of personality traits are relatively high (i.e. heredity must be a factor in personality)
what do family studies do
- correlate the degree of genetic relatedness among family members with the degree of personality similarity –> uses this because there are known degrees of genetic relatedness among family members
- if a personality characteristic is highly heritable, then family members with greater genetic relatedness should be more similar to each other than those who are less genetically related
- if personality characteristic is not heritable, then members should not be similar
what is the limitation of family studies
- family members who share genes typically share the same environment
- family members might be similar to each other because of shared environment, not shared genes
what are twin studies
- estimate heritability by looking at identical twins (share 100% of genes) compared to fraternal twins (share 50% of genes)
- can look at twins reared apart and examine differences/similarities
describe monozygotic twins
come from a single fertilized egg which divides into two at some point –> always the same sex
describe dizygotic twins
come from two eggs that were separately fertilized –> can be the same or opposite sex
what is the difference between dizygotic twins and regular siblings
- no more genetically alike
- dizygotic share the same womb and have same birthday
what are the assumptions made by twin studies
- if fraternal twins are just as similar as identical twins, then we can infer that a characteristic is not heritable
- if identical twins are more similar, this gives evidence for heritability
what is the heritability formula for twin data
- heritability^2 = 2(Rmz + Rdz)
what is an important assumption of the twin method
- equal environments assumption
- environments experienced by identical and fraternal twins are equally similar
how can the assumption of equal environments in twin studies be validated
- examine twins who have been misdiagnosed as identical or fraternal –> parents believed they were the opposite type of twin
- findings supported the validity of the equal environments assumption –> environments do not seem to be any more functionally similar
what have behavioural genetics shown about mental toughness
- combines hardiness and confidence
- overall heritability coefficient of .54 –> genes account for 54% of variance
- commitment component demonstrates greatest degree of environmentality –> may be most responsive to improvement/training
- big 5 traits have similar levels of heritability
what are adoption studies
- one can examine correlations between adopted children and their adoptive parents (no genes shared) –> observed similarities gives evidence for strong environmental influence
- can examine relations between adopted children and their genetic parents (who had no influence on their children’s environments) –> evidence for heritability if they are similar
what advantage does adoption studies have over twin studies
gets around the equal environments assumption –> un-confounds genetic and environmental causes
what are some problems with adoption studies
- assumption of representativeness –> assume that adopted children, birth parents and adoptive parents are representative of the population
- selective placement –> adopted children may be placed with adoptive parents who are similar to their birth parents, which might inflate correlations
describe the assumption of representativeness
- assume that adopted children, birth parents and adoptive parents are representative of the population
- assumes couples who adopt children are no different from couples who do not adopt children
- studies have shown this assumption holds for cognitive abilities, personality, education, etc.
selective placement
- adopted children may be placed with adoptive parents who are similar to their birth parents, which might inflate correlations
- does not seem to be this problem in actual studies
what is the most powerful behavioural genetic designs
- twins reared apart –> combines twin study and adoption study
- this is rare
what has been found on twin studies vs adoption studies examining heritability in personality traits
- substantial heritability for neuroticism and extroversion
- heritability is lower in adopted children for extraversion and neuroticism, correlation between adoptive parents/children is zero –> little direct enviornmental influence
summarize the findings on heritability of activity level and temperament
- 50% heritability for all temperaments
- 40% heritability for activity level
describe the heritability of “psychopathic” personality traits
- all show moderate to high heritability
- higher in MZ compared to DZ twins
is heritability of personality observed in other non-human species
yes studies on chimps also show high heritability of traits
summarize the findings on heritability of personality traits
- heritability of personality is heavily responsible for the fact that personality traits remain fairly stable over time
- yield heritability estimates of approximately 50 percent
what did the Minnesota Twin Study show on heritability of traditional attitudes/preferences
- traditionalism (favouring conservative values over modern values) had heritability of .59
- more range for other categories of social values (e.g. .63 for prosocial values)
- adoption studies show genetic influence on conservative attitudes
describe how genes influence occupational preferences
occupational preferences such as desire for competition and wealth can
lead to choosing occupations in which more status and income are actually achieved
what attitudes and beliefs appear to have zero heritability
- belief in God
- involvement in religious affairs
- attitudes towards racial integration
- the heritability of religiousness increases in adulthood to 44%
describe the findings of heritability of sexual orientation
- looked at twin and adoptive studies of gay men and lesbian women
- heritability estimates ranged from 30-70%
what are some findings suggesting biological influences of sexual orientation
- one study found that an area of the hypothalamus that regulates male-typical sexual behaviour was smaller in gay men
- another study found evidence sexual orientation is influenced by a gene on the X chromosome
–> these studies haven’t replicated
what are some weaknesses on studies looking at heritability of sexual orientation
- small samples and no replications
- neglects correlates of sexual orientation (e.g. childhood gender nonconformity is associated with sexual orientation, and is heritable)
describe concordance rates in sexuality
probability that if one twin is gay, the other will be gay has high concordance rates (40-50%)
describe the heritability of drinking and smoking
- heritability in smoking are consistently high
- mixed findings for regular drinking habits –> heritable in boys but not girls, others show heritable in both
- strong heritability for alcoholism and also conduct disorder
what is the heritability estimate for propensity to marry
68% –> linked to personality traits in partners
what is the heritability estimate for marital satisfaction
50% –> personality characteristics play a role in their own and their partners marital satisfaction
what are shared vs non-shared environmental influences
- shared = experienced similarly
- non-shared = experienced differently
–> think of siblings as an example
what has more influence over personality: shared or non-shared environmental characteristics
- shared environment has little to no impact on most personality variables –> even if siblings grow up together, what happens in their shared environment does not cause them to be similar
- non-shared environment does have an influence –> critical environmental influences on personality appear to lie in the unique experiences of individual children
what has more influence over personality: shared or non-shared environmental characteristics
- shared environment has little to no impact on most personality variables –> even if siblings grow up together, what happens in their shared environment does not cause them to be similar
- non-shared environment does have an influence –> critical environmental influences on personality appear to lie in the unique experiences of individual children
what two unique (non-shared) experiences are influential over personality
- different peer influences
- might be that there are so many environmental variables that impact personality that each one along only accounts for a tiny bit of variance
what does shared environment account for
- several personality clusters in the “adjustment” domain –> antisocial behaviour, depressive symptoms, autonomous functioning
- some suggest that shared environment might influence personality more than was previously thought
what is genotype-environment interaction
- differential response of individuals with different genotypes to the same environments –> e.g. introverts perform well on cognitive tasks when there is little stimulation in the room
- individual differences interact with environment to affect performance
describe a genotype-environment interaction in children who experienced childhood abuse
- children with low levels of MAOA who experienced abuse developed conduct disorders, antisocial personality, etc.
- high levels of MAOA = less likely to develop aggressive antisocial personalities
- exposure to same environment (abuse) impacts different genotypes differently
what is genotype-environment correlation
differential exposure to individuals with different genotypes to different environments –> e.g. child with genotype for high verbal ability might be exposed to more books because parents reinforce it
what are the three types of genotype-environment correlations
- passive g/e correlation
- reactive g/e correlation
- active g/e correlation
Passive genotype–environment correlation
parents provide both genes and the environment to children, but children do nothing to obtain that environment (e.g. correlation between verbal ability and number of books in home, as supplied by highly verbal parents)
Reactive genotype–environment correlation
parents (or others) respond to children differently depending on the child’s genotypes –> if babies like to be touched they will smile and giggle, so parents respond by continuing to touch the baby (people react differently to children depending on their dispositions)
Active genotype–environment correlation
person with a particular genotype creates or seeks out a particular environment (e.g. intellectual people seek out intellectually stimulating environments) –> “niche picking”
describe the two ways genotype-environment correlations can influence a person
- positively (environment goes with their genotype)
- negatively (environment goes against their genotype, e.g. telling active kid to calm down)
describe the relationships between personality and perceptions of family environment
- they are genetically mediated –> perceived environment in which individuals were raised was largely due to heritable personality traits (e.g. experiencing a cohesive family upbringing was explained by constraint and negative emotionality)
- calm personalities might be promoting family cohesion, or might be impacting how they remember their childhood
what is molecular genetics
designed to identify the specific genes associated with personality traits –> identify whether individuals with a particular gene/allele have higher/lower scores on a particular trait than those without the gene
what is the DRD4 gene
located on chromosome 11 and codes for dopamine receptors –> commonly examined in its associations with novelty seeking
describe the found relationships between the DRD4 gene and novelty seeking
people with long repeat versions of the gene were higher on novelty seeking –> these people are relatively unresponsive to dopamine thus need novelty to get a “buzz”
–> note there have been mixed findings in replications, especially because association is small and might be involved with several other genes (e.g. 7R allele)
what are GWAS
genome wide association studies –> can rapidly examine the entire genome for links with personality
describe the environmentalist view of behavioural genetics
view that personality is determined by socialization practices (e.g. parenting style)
