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What is behavioural genetics? Sources of variance Common designs
Specific developmental psychology questions
– Genes and change – Does heredity change over time? – What initiates development? – Genotype and Environment
What is behavioural genetics? (1)
How can Differences among people be explained? Do people differ from each other because of
– Environmental differences they were raised in different families? they made different unique experiences?
– Genetic differences –
they are genetically unique?
What is behavioural genetics? (2)
– Environment – Heredity
proportion of the total variance that can be explained by genetic variance
– How much does each factor contribute? – How does the 2 factors work together?
MZ raised apart
– – – – Genetic identical Separated, raised apart Compare personality characteristics Similarities can only be due to genetic similarities
MZ - DZ comparison
– MZ and DZ raised together – Share environment, family, parental style… – But 1 huge difference:
MZ genetically identical DZ share ~50% of their genes (=all siblings)
– Compare personality characteristics – Greater MZ similarities must be due to greater genetic similarities
– Genetic unrelated siblings in a family – Share environment, family, parental style… – Compare personality characteristics – Similarities can only be due to shared environment
Id en t ic al
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Correlation on intelligence test scores (adapted from Dworetzky, 1996; Bouchard & McGee, 1981)
/T og et he Id r en t ic al /A pa rt Pa re nt /C Fr hi at ld er na l/ T og et Si he bl in r gs /T og et he Si r bl in gs Ad /A op pa te rt d Si bl in Ad gs op /.. te . d Pa re nt /C hi ld
How much does each factor contribute?
– Kinship studies
Texas adoption project (Horn, 1983) Minnesota twin study (Bouchard et al, 1990)
– MZ heritability correlation .78
Pedeson et al (1992)
– MZ heritability correlation .78
An example: Intelligence
– correlation with biological mother .28 – correlation with adoptive mother .15
– 13,000 twin pairs. Intelligence correlation .86 for MZ, .55 for DZ .
Problems with heritability and concordance (1)
Heritability estimates may be higher in population with shared environment. MZ twins raised together show more highly correlated intelligence scores than those raised apart.
– So need to conduct research with twins raised apart so as not to overestimate heritability – – hard to find.
Problems with heritability and concordance (2)
Do twins represent the range of environmental differences in population even if raised separately?
– More likely to be placed in ‘good’ homes by social services.
Heritability estimates have been used to suggest ethnic differences in intelligence due to genetics
– there are also economic and cultural differences.
Are these measures useful?
– How do traits develop? – How can we influence their development?
How do heredity and environment work together?
Reaction range (Gottesman, 1963) Canalization (Waddington, 1957, 1966). Genetic-environmental correlation (Plomin et al, 1994).
Reaction range (from Berk, 2000)
Genes and Change
Genome can’t change, but gene activity can
– Gene activity can switch on and off
Genes are only relevant at certain times
– language effecting genes only relevant from 2nd year on – Genetic influences can be age-specific
Genetic influences can be changed
– e.g. Phenylketonuria PKU
Some studies with kids show influence of the shared environment Most studies with adolescents and adults don’t
– Siblings: growing up and growing apart
Heredity increases over time Influence of shared environment decreases
Development of heritability and environment (from Plomin et al, 2001)
What initiates Development?
Genes play a role in initiating change
– e.g. Puberty is not an environmentally influenced change
Longitudinal studies of individual development
– Study development of MZ and DZ twin pairs – Observe synchronicity and compare MZ-DZ pairs – MZ more synchronic than DZ
genetic influenced pattern
Genotype and Environment
– Plomin et al. (1977, 1994) identified 3 types: Passive
– Kids receive genotype and family environment
– People react to individuals specifically
– Individuals seek or create environments
Passive, evocatice and active correlation (from Shaffer, 2002)
You should be able to Identify the rationale of behavioural genetics Correctly describe common designs Summarise behaviour genetic research results Present specific developmental psychology questions