L1 NEUROCLIN II: Behavioural Genetics I

To be able to critically evaluate the concept of heritability in behavioural genetics: What do we mean by heritable/hereditary? What ‘things’, as psychologists, might we be interested in investigating the heritability of ? How would we investigate this?

heritability

an estimate of how much variance in some characteristic within some population is due to differences in heredity

heritability: range

• varies between 0 and 1 (0 and 100%)

• 0.5 = intermediate

big 5

1. extraversion

2. agreeableness (aggression)

3. conscientiousness

4. neuroticism

5. openness

big 3

1. positive emotionality

2. negative emotionality

3. constraint

heritability statistic for personality traits (adult samples)

heritability statistic for psychological interests:

• realistic

• investigative

• artistic

• social

• enterprising

• conventional

monozygotic twins

• 1 egg

• identical

• 100% shared genetic variation

• if trait was completely heritable, mz twins wld score same

dizygotic twins

• 2 eggs

• non identical

• fraternal

• 50% shared genetic variation- same as any other siblings sharing both parents

heritability graphs for mz and dz

how is heritability calculated (not actual eq)

• comparing the correlation coefficients of identical and non-identical twins for a particular trait

→ know identical share all variation, non identical share half genetic variation

→ heritability is twice the difference between correlations for identical minus non identical twins

heritability ‘equation’ using mz and dz correlation coefficients

heritability = 2 x ( identical correlation coeffient - non identical correlation coefficient)

heritability = 2 x ( r_mz - r_dz)

what is the heritability statistic for each:

1. childhood fatigue

2. ADHD

3. bulimic symptoms

4. depression (unipolar)

5. manic depression (bipolar)

6. autism

7. schizophrenia

1. 2 x (0.8 - 0.6) = 0.4

2. 2 x (0.78 - 0.32) = 0.92

3. 2 x (0.3-0.25) = 0.1

4. 2 x (0.75 - 0.35) = 0.8

5. 2 x (0.92 - 0.5) = 0.84

6. 2 x (0.8 - 0.4) = 0.8

7. 2 x (0.7 - 0.3) = 0.8

variance equation

V_p = A² + C² + E²

V_p = A² + C² + E²

• explain each variable

V = variance of a trait

A = genetic component

C = common or “shared” environment (anything in the env that makes traits similar across twin pairs)

E = the “non-shared” environment (anything in the environment that makes traits dissimilar across twin pairs)

r_mz =

A² + C²

r_dz =

½ A² + C²

A² =

2(r_mz - r_dz)

• additive genetic influence (heritability)

what does heritability look at

variance (differences) between individuals

what is heritability specific to

the population in which it is calculated

what does high heritability not imply

that the environment does not alter the trait, particularly for the individual

sharing highly similar environment → heritability estimates will be high

heritability of general cognitive ability

increases linearly from childhood to young adulthood

complexities with heritability according to Flynn, (2001)

multiplier effect

multiplier effect

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 the tendency (Flynn, 2001)

complexities with interpretations of behavioural genetics

• change with age

• change over time

• multiplier effect

tobacco use + heritability

• example of heritability complexity

• Pinel said tobacco use heritability estimate 65%

• but then

• 2-3 ppl admitted to smoking in the 1003 lecture

how can it be genetic → have genes changed? probs not

• need the environment of smoking no matter how genetically predisposed you are

• nicotonic receptor gene variants influence susceptibility to heavy smoking

• environment + genes- risk taking, substance use, addictive personality, peer pressure/antisocial peer group

misrepresentations in popular media

• genetics research often overgeneralised outside of population statistics taken in, heritability stats shown as proof of geneticism with disregard to shared environment or associative nature

• eg. independent report on michael gove holding talks with iq genes e.g. saying genes account for 70% of a child’s cognitive abilities

• dangerous, eugenics, misrepresentative, social sensitivity

→ behavioural genetics CANNOT tell us about an individual

• does not account for up to 70% of childs abilities, but 70% of variation in abilities within that population can be attributed to heritability

• tests with knowledge components not cognitive

• lots of routes for heritability peer groups etc

• this cannot be inferred from behavioural genetics analysis- that believe any child from background can achieve

heritability values that are:

1. high

2. intermediate

3. low

1. 0.6

2. 0.4

3. 0.2