PSY2003 S2 W1 Behavioural Genetics I Flashcards
What do we mean by heritable/hereditary?
In Behavioural Genetics
Estimate of how much variance in some characteristic within some population is due to differences in heredity.
Varies between 0 and 1 (i.e. 0 and 100%)
0.5 intermediate.
The rest of the variance is due to environmental factors.
How do we investigate heritability ?
Twin studies.
No as many twins that have been separate nowadays as it is considered slightly unethical but in the 1950s 1960s it was very common.
Who is Thomas Bouchard?
Twin studies/heritability, focused on personality traits.
What are the problems with anecdotal evidence about twins?
Research might keep looking for things that are similar.
What do we need to look at in twin studies?
Actual data from twins to calculate heritability
What are the problems with just looking at identical twins?
In modern studies they might not have been reared apart. Environment can also have an affect even when separate.
What is a strong positive correlation?
all the data is in a linear pattern on the graph [ / ]
What is a weak positive correlation?
When the data is in a somewhat linear line
What is no correlation?
When the data is spread out with no linear pattern visible
correlations
What is involved in twin studies?
Observing corelation coefficients.
Bioploar has hgihest heritability, because the Mz twins line is closest to 1.
Bulimic symptoms seem to not be heritable because the corelation coefficient is low and similar to that of Dz twins.
In a corelation twin study what does two similar values (Dz / Mz twins) suggest?
That the envionrment is causing the variance
How is heritability calculated?
comparing the correlation coefficients of identical and non-identical twins for a particular trait.
What is the difference in heritability between identical (Mz) and Non-identical (Dz) twins?
We know that identical twins share all their genetic variation.
We know that non-identical twins share 50% of their genetic variation.
The heritability is twice the difference between the correlations for identical minus non-identical twins.
What is the equation for measuring heritability?
Vp=A^2+C^2+E^2
What does the V, A, C and E mean in the heritability equation?
V is the variance of a trait
A is a genetic component/heritability – additive of genetic component
C is the common or shared environment
E is the non-shared environment
Equation of Heritability
Are E and C whether varaince is shared ?
C and E is not actually whether it is shared per se. C is anything in the environment that makes the traits similar across twin pairs. E is anything in the environment that makes the traits dissimilar across twin pairs
What is the heritability equation for Mz Twins?
r[MZ]=A^2+C^2
What is the heritability equation for Dz Twins?
r[DZ]=1/2A^2+C^2
How do you rearrange the heritability equation?
A^2=2(r[MZ]-r[DZ])
‘The heritability is twice the difference between the correlations for identical minus non-identical twins’
Example: Table 1: .6 -.3 = .3 x 2 = .6
What is heritability in a population?
Heritability is ‘specific’ to the population in which it is calculated.
It looks at variance (differences) between individuals.
High heritability does not imply the environment doesn’t alter that trait, particularly for the individual.
What does high heritability does not imply?
High Heritability does NOT imply environment does NOT play a role
If a Group of individuals share a highly similar environment, what effect does this have on the heritability estimate of a characteristic?
heritability estimate will be high
What are two explanations of the complexities with heritability?
Multiplier Effect (Flynn, 2001).
More complexities with interpretations of behavioural genetics.
What is the Multiplier Effect ?
Flynn, 2001
‘If Genetic or prenatal influences produce even a small increase in some activity, the early tendency will change the environment in a way that magnifies that tendency’
