6: GENETICS Flashcards
Behavioural Genetics
Study of genetic and environmental influences on human behaviour. How much are we influenced by those differences?
> Worry that findings will be used or misused to support particular political agendas. If genes cause thrill seeking, should delinquents still be held responsible?
The Nature-Nurture Debate
Levels of analysis: of the individual & the level of a population
> At the individual level, there is no nature-nurture debate. Every indivisual contains a unique constellation of genes. The genes require environments during one’s life to produce a recognizable person
> At the population level, it is important to ask the nature-nurture debate.
Heritability
The degree to which genetic differences among us cause differences in an observed property
Phenotypic Variance (observed)
Genotypic Variance (differences in the total collection of genes
- A heritability of .2 means 20% of the phenotypic variation is attributable to genotypic variation
- Cannot be applied to a single individual for a single reason for a trait
- It is not constant and applies to only one population at a time in a particular environmental set
- Depends on the range of environmental differences and the range of genetic differences
Environmentality: Percentage of observed variance in a group of individuals that can be attributed to environmental differences
Family Studies
> Correlate the degree of genetic relatedness among family members with the degree of personality similarity
- If a personality characteristic is highly heritable then family members with greater genetic relatedness should be more similar
Twin Studies
> If identical twins are substantially more similar to each other than are fraternal twins on a given characteristic, then this provides evidence that is compatible with a heritability interpretation. In fact, studies have shown that identical twins are more similar than fraternal twins in dominance, height, and the ridge count on their fingertips
For dominance: Identical twins correlate at +.57, Fraternal at +.12
For height: Identical twins correlate at +.92, Fraternal at +.48
Calculating Heritability: Twin Method
heritability2 = 2 (rmz - rdz)
Rmz → the correlation coefficient between monozygotic twins
Rdz → the correlation between dizygotic twins
Equal Environments Assumption of calculating heritability
Assumes environments experienced by identical twins are no more similar to each other than the environments experienced by fraternal twins.
- Twins mistakenly seen as identical that are fraternal showed that the parent’s beliefs and labelling of the twins did not affect their actual similarity in personality and cognitive measures. However labelled, the environment’s experiences are not functionally similar to those of fraternal twins.
Adoption Studies
> If we find a positive correlation with whom they’ve had no contact with, then provides evidence for heritability.
- Adoption studies allow to get around the equal environment assumption
Problem with representativeness: assuming they represent the general population
- Assume couples who adopt children aren’t any different from couples who don’t adopt children
Problem of Selective Placement: If adopted children are placed with adoptive parents who are similar to their birth ones this may inflate the correlations
Drinking & Smoking & Genetics
> Regarded as behavioural manifestations of personality dispositions like sensation seeking, extraversion and neuroticism
MZ twin who smoked was roughly 16 times more likely than an MZ twin who did not smoke to have a twin who smoked. The comparable figures for DZ twins were only a sevenfold increase, suggesting evidence of heritability.
Most studies, however, show moderate heritability for both sexes, ranging from .36 to .56
Heritability studies of alcoholism, as opposed to everyday drinking habits, show even stronger heritabilities.
DRD4 Gene
- Codes for dopamine receptors
- Longer repeat versions were found to be higher on novelty-seeking
- highly responsive to whatever dopamine is present, so tends to not seek out novel experiences which might boost dopamine to uncomfortable levels
- Linked with mother’s reports of their children’s problems with aggression, but was not linked with observed behavioural measures of aggression
7R allele of the DRD4 is linked with engaging in financial risk
genome-wide association studies (GWAS), which can rapidly examine the entire genome for links with personality
> it appears likely that personality traits are linked to such a large number of genes that each accounts for only a small effect on personality. This has led to measures of polygenic risk scores, which are mathematical sums of many genetic variants. Can be used for well-being (depression, neuroticism)
McLaffery (2006)
- Exclusivity: only nature and nurture
* 2.Universality: applies to all human traits
* 3. Complementary: one or the other
either genetics, environment or their
interaction
