5-6 Genes and Behaviour

Question 1

What is heritability (h-squared)?

Answer 1

A desciptive statistic that indexes the degree of population variation in a trait that is due to genetic differences.

Question 2

What are the three components in the ACE model?

Answer 2

A – additive genetics
C – common (shared) environment
E – unique (non-shared) environment

Question 3

What are three common criticisms of the twin study model?

Answer 3

1. Heritability values are strongly tied to the populations in which they were gathered. In more diverse environments, we’d expect the degree of heritability to go down.
2. Most twins are raised under highly similar conditions, which would tend to boost the contribution of genetics to variance in a trait – as environment is being held constant.
3. DZ twins are more different than MZ twins, and so would elicit more different reactions from the environment. This would also boost the contribution of genetics – as the A value is calculated as 2(rMZ − rDZ) .

Question 4

What equation is used to calculate ACE?

Answer 4

A = 2(rMZ − rDZ) 
C = 2rDZ − rMZ
E = 1 − rMZ

Question 5

What are the environmental and genetic contributions to:

1. Literacy and language at 5 years (Byrne et al. 2009)
2. Social cognition at 5 years (Hughes et al. 2005)
3. Child psychopathology (Burt, 2009)

Answer 5

1. Clear genetic influence on literacy and language. Shared environment affects only semantics/vocab
2. Social cognition at 5 years shows a clear shared environmental influence (but not a genetic influence)
3. Child psychopathology shows both for all domains except for ADHD (no shared environmental effect).

Question 6

Turkheimer (2000)
Human developmental social science is difficult – equally so for the genetically and environmentally inclined – because of the confluence of two conditions…

Answer 6

1. Behaviour emerges out of complex, non-linear processes

2. Ethical considerations prevent us from bringing most human developmental processes under experimental control.

Question 7

Heritability depends on how _________ a population is. If there’s no diversity in __________ information, everything is environmental; if there’s no __________ difference, everything is genetic.

Answer 7

Heritability depends on how heterogeneous population is. If there’s no diversity in genetic information, everything is environmental; if there’s no environmental difference, everything is genetic.

Question 8

What is the viewpoint Turkheimer calls ‘interactionism’ or ‘developmentalism’?

Answer 8

No trait can develop without both genetic and environmental inputs –it requires an interaction between the two. So growing to a particular height is no more genetic than learning to play the oboe.