Lecture 4: Genetics and Peronsality Flashcards
What is a Genome?
Genome refers to the complete set of genes an organism possesses. The human genome contains between 20,000 and 30,000 genes. All these genes are located on 23 pairs of chromosomes. Each person inherits one set of each pair of chromosomes from the mother and one set from the father
What is the human genome project?
is designed to sequence the entire human genome—i.e., identify the particular sequence of DNA molecules in the human species . But identifying sequence of DNA molecules does not mean identifying the function of each molecule.
Are most genes the same or different for humans?
- Most genes in a human genome are the same for all humans
- Small number of genes are different for different individuals, including genes that indirectly code for physical traits and for personality traits
What do behavioural geneticists do?
Behavioral geneticists attempt to determine the degree to which individual differences in personality are caused by genetic and environmental differences
What is highly controversial about studying genes and personality?
- Ideological concerns about findings being misused (Many people worry that findings from behavioural genetics will be used (or misused) to support particular political agendas. If individual differences in thrill seeking, for example, are caused by specific genes, then does this mean that we should not hold juvenile delinquents responsible for stealing cars for joy rides?)
- Concerns about renewed interest in eugenics (Many people are concerned that findings from genetic studies might be used to support programs intended to prevent some individuals from reproducing or, even worse, to bolster the cause of those who would advocate that some people be eliminated in order to create a “master race.”)
What is the important take home message about studying personality and genes?
Finding that a personality trait has a genetic component does not mean the environment is powerless to modify trait
What are the 2 goals of behavioural genetics?
1) Determine % of individual differences in a trait that can be attributed to :genetic differences, environmental differences
2) Determine the ways in which genes and environment interact and correlate with each other to produce individual differences
What is Heritability?
Proportion of observed variance in group of individuals that can be explained or accounted for by genetic variance. Proportion of the phenotypic variance that is attributable to genotypic variance
What is environmentality?
- Proportion of observed variance in group of individuals attributable to (non-genetic) environmental variance.
- If heritability of a personality trait is .70, then genes account for 70% of observed (phenotypic) variation, and environment accounts for 30%
What are some misconceptions about heritability?
-Heritability CANNOT be applied to single individual
(Only relevant for discussion of group-level variation)
-Heritability is NOT constant or immutable (can change over time and can be different in different populations)
-Heritability is NOT a precise statistic (Based on correlations, which by nature have degree of imprecision and fluctuation across samples)
What are the 4 behavioural genetics methods?
1) Selective Breeding
2) Family Studies
3) Twin Studies*
4) Adoption Studies
What is selected breeding?
- Cannot be ethically conducted with humans
- occurs by identifying the dogs that possess the desired characteristic and having them mate only with other dogs that also possess the characteristic.
- Selective breeding studies of ….
- Can only occur if a desired trait is heritable
What are family studies?
- Correlates the degree of genetic overlap among family members with the degree of similarity in personality trait
- If a trait is highly heritable, family members with greater genetic relatedness should be more similar to one another on the trait than family members who are less closely genetically related
What is the problem with family studies?
- Members of a family who share the same genes also usually share the same environment—confounds genetic with environmental influences
- Thus, family studies are never definitive
What are twin studies?
- Estimates heritability by gauging whether identical (monozygotic or MZ) twins, who share 100% of genes, are more similar than fraternal (dizygotic or DZ) twins, who share only 50% of genes
- If MZ twins are more similar than DZ twins, this provides evidence of heritability
What are the two assumptions of the twin method?
- Equal environments assumption: environments experienced by identical twins are no more similar than those experienced by fraternal twins. Assumption has largely been supported; sometimes violated
- Representativeness assumption (twins = rest of pop.). Questionable in some ways (prematurity, low birth weight)
What are adoption studies?
- Positive correlations on traits between adopted children and adoptive parents provide evidence of environmental influence
- Positive correlations between adopted children and genetic parents provide evidence of genetic influence
What are the assumptions of adoption studies?
- Adoption studies are powerful because they get around the equal environments assumption (no need for this assumption)
- But, assumption that adopted children and their adoptive and genetic parents are representative of the general population
What is a potential issue of adoption studies?
Potential issue if selective placement of adopted children. Research suggests this is not occurring
What is an ideal design?
- Design that combines strengths of twin and adoption studies = Twins Separated at Birth
- Correlation between identical twins reared apart is a direct index of heritability.
What are the advantages of each of the behavioural genetics methods?
- Selective breeding: can infer heritability if breeding works
- Family studies: provide heritability estimates
- twin studies: provide both heritability and environmentality estimates
- Adoption studies: provide both heritability and environmentality estimates; get around the problem of equal environments assumption
What are the limitations of each of the behavioural genetic methods?
- Selective breeding: is unethical to conduct on humans
- Family studies: Violate equal environments assumption
- Twin studies: sometimes violate equal assumptions
- Adoption studies: adopted kids may not be representative; selected placement may be a problem if it occurs
What are some of the areas of major research findings?
- personality traits
- attitudes and preferences
- drinking and smoking
What does behavioral genetic research show about personality traits?
- Summaries of behavioral genetic data show heritability estimates for major personality traits (Big 5 traits) of ~ 50%
- Moderately heritable
- Heritability of personality is heavily responsible for fact that personality is stable over time
- But, 50% heritability also means that substantial portion of variance in personality is related to the environment
