behavioural genetics 1 Flashcards
what is heritability
an estimate of how much variance in some characteristics within a population is due to differences in heredity
between 0 and 1
(0.5 is intermediate)
examples of heritability - big 5, psych interests, twins
big five:
extraversion = .54
most around .5
psychological interests:
most around .3-.4
.5 = equal genes and environment
lots of anecdotal clinical evidence of similarities in twins with personality
how is heritability calculated
comparing the correlation coefficients of MZ and DZ twins for a trait
heritability = 2x difference between correlations for MZ minus DZ twins
equation for variance
Vp = A²+C²+E²
V = variance of a trait
A = genetic component
C = common/shared environment
E = non-shared environment
be careful with C+E:
C = anything in the environment which makes traits similar in twin pairs
E = anything in environment that makes traits dissimilar in twin pairs
correlation in MZ twins equation
rMZ = A²+C²
A = genetic component
C = common/shared environment
correlation in DZ twins equation
rDZ = 1/2A²+C²
A = genetic component
C = common/shared environment
equation to calculate genetic component of twins
A² = 2 (rMZ - rDZ)
the heritability is twice the difference between the correlations for MZ minus DZ twins
heritability - what it is and facts about it (4)
specific to the population in which it is calculated
looks at variance between individuals
high heritability does NOT mean environment doesn’t alter the trait - particularly for the individual
heritability can change over time - both between and within cohorts (so some research can be influenced by cohort effects)
what does high heritability mean about the environment influences + example
high heritability does NOT mean environment doesn’t alter the trait
EXAMPLE:
two plants grown with identical seeds grow differently when one is planted in normal nutrient soil and the other in deficient soil - variance is due to the environment not genetics
similar environments = high heritability estimate
twins early development study
used data from many twin studies on behavioural genetics and mapped to where they came from
for a wide range of developmental traits
colour map to show hereditability levels in different areas - quite big differences depending on where people live
different spreads of heritability numbers depending on characteristic
highest heritability seen around London and south coast - higher levels seen more centrally in cities
heritability may appear higher if people share the same environment - and from different environments may make the environment seem to play a bigger role
trying to find what causes differences in variance e.g. socioeconomic status - large variation in London of high and low SES
how does heritability of cognitive ability change with age
linear increase from childhood to young adulthood - increased heritability with age
multiplier effect
Flynn (2001)
if genetic or prenatal influences produce even a small increase in some activity, early tendencies will change the environment in a way that magnifies that tendency
e.g. a young kid who is good at football will do more training and become great at it
e.g. a smart kid will do harder problems and get even better
this is an example of a complexity with heritability
heritability and tobacco use
Pinel states heritability estimate of 65% with tobacco use
but massive variation with people who smoke - cultural variation, what is acceptable at the time
becoming less acceptable so less smoking - how is this heritable? genes probably haven’t changed so must be another cause of this change in incidence
heritability is specific to the population in which it is calculated
psychology and behavioural genetics
psychological side
e.g. personality differences and characteristics such as extraversion - how does this play into behavioural genetics
complex behaviours - such as tobacco use
has heritability but also influenced by peers and environment
need the smoking environment in addition to genetics in order to start
issue with using twins for concordance rates
if both don’t do the behaviour, concordance will still be 100% - unclear if they do or don’t do behaviour
also personality differences e.g. risk taking, addictive personality, willingness to take any substance
could be in an anti-social peer group
