Behavioural genetics Flashcards
In terms of twin studies, what is ‘correlation’?
Correlation refers to the extent of the systematic relationship between twin 1 and twin 2 on a certain trait.
MZ twins will have a higher correlation, while DZ twins will be less correlated with one another.
Correlations between twins are also typically linear. Eg: height. Whether you’re short or tall, your twin will likely be the same height as you.
In terms of twin studies, what is ‘variation’?
Variation refers to the way the points are distributed on the measurement scale.
Typically, MZ and DZ twins will have the same range of variation (ie: the same highest and lowest score), but the way in which the points between the highest and lowest are distributed will differ.
What is a common environment?
An environment/event that both twins experience/are equally influenced by (eg: parenting style, number of siblings)
What is a unique environment?
An environment/event that only one twin experiences, or an environment/event that both twins experience but it influences them differently (eg: friends at school)
What is the correct, final heritability index model?
P (=1) = additive genetics (A) + common environment (C) + unique environment (E)
What are the formulae for rMZ and rDZ
rMZ = h squared + C
rDZ = 1/2h squared + C
What is the formula for h squared, in terms of rMZ and rDZ?
h squared = 2(rMZ - rDZ)
What is the formula for C, in terms of rMZ and/or rDZ?
C = rMZ - h squared
What is the formula for E, in terms of rMZ and/or rDZ?
E = 1 - rMZ
What are the four main criticisms of the twin model?
Heritability estimates are strongly linked to the population they’ve been drawn from. In more diverse populations, we’d expect heritability to go down.
Most twins are raised in a very similar environment, so there is little variation in the unique environments.
It assumes there is no assortative mating in the population
It does not indicate the degree of genetic influence on the development of a trait - it’s just about the proportion of variation in phenotype due to variation in the genotype (ie: it’s incorrect to say .6 heritability for height means that you get 60% and your height from your parents and the other 40% from the environment)
Explain the background and findings of the meta-analysis on internalising and externalising psychopathology prior to adulthood
Traditional twin studies had found that the majority of the effects of psychopathology were due to non-shared environment and additive genetics, there was very little effect of shared environment found.
It was thought shared environments may be more important prior to adulthood and in more extreme environments.
The meta analysis found a modest-moderate effect of shared environment on all psychopathological outcomes, except attention deficit/hyperactivity problems.
Non-shared environment had a profound effect on all outcomes, including ADHP.
This provides more evidence that parenting styles and behaviours have a significant impact on psychopathological outcomes of children. Over protective and controlling parents typically cause anxiety in children, while hostile parents and parents who don’t set clear boundaries lead to children with more externalising problems. Externalising problems in children are the biggest predictor of all psychological problems later in life.
What is the missing heritability problem?
The missing heritability problem refers to our inability to find the source of certain genetic variations.
We know that all traits are heritable, but we don’t know much about the exact genetic variables that are associated with this heritability.
Gene-disorder associations are rare, and even when they are identified, genome-wide studies indicate that only tiny proportions of the phenotypic variance is attributable to common genetic variations
What might be some reasons for the missing heritability problems?
1) We are not looking at the correct genes.
Perhaps the hypotheses of our research is wrong.
Perhaps genes we are looking at are not functioning the way we expect them to function
Perhaps the genes we are looking at are functioning in a similar way to other genes or other gene-gene interactions.
Perhaps proteins are not doing what we thought they would do. Or, proteins are doing what we thought they would do, but not affecting the brain in the way we thought they would.
2) We are not looking at the right samples.
Perhaps there are overlaps between different phenotypes with different aetiologies. We need to specifically describe the phenotype first.
Perhaps there are different distributions of genotypes in different ethnicities
Perhaps the range of descriptives is too large. Some developmental disorders may not be clear until a certain age eg: autism
3) We are not thinking about it in the right way
We have already mentioned gene-gene interactions, perhaps we need to keep looking there!
Explain interaction and mediation in terms of studying and exam performance
It is without doubt there is an interaction between how much you study and how well you perform on the exam. However, this is mediated by practice exams ie: the interaction between studying and exam performance is caused by the number of practice exams you do
Explain moderation in terms of genetic interaction effects
A genotype (or genotypic effect) may moderate the relationship between and environmental independent variable and a dependent variable. It may strengthen, weaken or change the direction of the relationship
