Behavioural Genetics

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Behavioural Genetics
Steve Croker Room C009 Ext. 2081 s.croker_at_derby.ac
.uk
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Outline

• 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

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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?

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What is behavioural genetics? (2)

• Role for
• Environment
• Heredity
• proportion of the total variance that can be
  explained by genetic variance 
• 2 questions
• How much does each factor contribute?
• How does the 2 factors work together?

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Designs (1)

• 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

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Designs (2)

• 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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Correlation on intelligence test scores (adapted
from Dworetzky, 1996 Bouchard McGee, 1981)
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How much does each factor contribute?

• Heritability estimates
• 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
• 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)

• 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)

• 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?

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How do heredity and environment work together?

• 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

• Genome cant 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

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Heredity Development

• Some studies with kids show influence of the
  shared environment
• Most studies with adolescents and adults dont
• 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?

• 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

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Genotype and Environment

• 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