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Behavioural Genetics

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					Behavioural Genetics

Steve Croker Room C009 Ext. 2081 s.croker@derby.ac.uk

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Outline
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What is behavioural genetics? Sources of variance Common designs

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Specific developmental psychology questions
– Genes and change – Does heredity change over time? – What initiates development? – Genotype and Environment
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What is behavioural genetics? (1)
How can Differences among people be explained?  Do people differ from each other because of
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– Environmental differences they were raised in different families?  they made different unique experiences?
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– Genetic differences –
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they are genetically unique?

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What is behavioural genetics? (2)
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Role for
– Environment – Heredity
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proportion of the total variance that can be explained by genetic variance

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2 questions:
– How much does each factor contribute? – How does the 2 factors work together?

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Designs (1)
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MZ raised apart
– – – – Genetic identical Separated, raised apart Compare personality characteristics Similarities can only be due to genetic similarities

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MZ - DZ comparison
– MZ and DZ raised together – Share environment, family, parental style… – But 1 huge difference:
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MZ genetically identical DZ share ~50% of their genes (=all siblings)

– Compare personality characteristics – Greater MZ similarities must be due to greater genetic similarities
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Designs (2)
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Adoption
– Genetic unrelated siblings in a family – Share environment, family, parental style… – Compare personality characteristics – Similarities can only be due to shared environment

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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)

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/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?
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Heritability estimates
– Kinship studies
Texas adoption project (Horn, 1983)  Minnesota twin study (Bouchard et al, 1990)
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– MZ heritability correlation .78
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Pedeson et al (1992)
– MZ heritability correlation .78

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Concordance rates

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An example: Intelligence
 Texas

Adoption Project

– correlation with biological mother .28 – correlation with adoptive mother .15
 Scarr

(1997)

– 13,000 twin pairs. Intelligence correlation .86 for MZ, .55 for DZ .
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Problems with heritability and concordance (1)
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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.

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Problems with heritability and concordance (2)
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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.

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Heritability estimates have been used to suggest ethnic differences in intelligence due to genetics
– there are also economic and cultural differences.

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Are these measures useful?
– How do traits develop? – How can we influence their development?
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How do heredity and environment work together?
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Reaction range (Gottesman, 1963) Canalization (Waddington, 1957, 1966). Genetic-environmental correlation (Plomin et al, 1994).

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Reaction range (from Berk, 2000)

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Genes and Change
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Genome can’t change, but gene activity can
– Gene activity can switch on and off

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Genes are only relevant at certain times
– language effecting genes only relevant from 2nd year on – Genetic influences can be age-specific

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Genetic influences can be changed
– e.g. Phenylketonuria PKU

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Heredity Development
Some studies with kids show influence of the shared environment Most studies with adolescents and adults don’t
– Siblings: growing up and growing apart
time

Heredity increases over time  Influence of shared environment decreases
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Development of heritability and environment (from Plomin et al, 2001)

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What initiates Development?
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Genes play a role in initiating change
– e.g. Puberty is not an environmentally influenced change

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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
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genetic influenced pattern

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Genotype and Environment
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Gene-Environment correlation
– Plomin et al. (1977, 1994) identified 3 types:  Passive
– Kids receive genotype and family environment
 Evocative

– People react to individuals specifically
 Active

– Individuals seek or create environments

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Passive, evocatice and active correlation (from Shaffer, 2002)

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Learning Objectives
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
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