Coeffecient of relatedness and predictions of complex genetic influences

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Coeffecient of relatedness and predictions of
complex genetic influences

• The coefficient of relatedness (r) between two
  individuals is defined as the percentage of genes
  that those two individuals share by common
  descent.
• MZ twins 1.0
• DZ twins 0.5
• Siblings 0.5
• Parents offspring 0.5
• Grandparents grand children 0.25
• If a behavioral trait is under complete genetic
  control would we predict that r total
  variability in the trait?

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Environmental hypothesis
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• Two major approaches used by behavior
  geneticists to study relative contributions of
  genes environment in the development of
  behavior
• Hold genetic make-up constant to study effects of
  the environment alone (VTVE)
• cross-fostering experiments twin studies
• Hold environment constant explore effects of
  genes alone (VTVG)
• selective breeding experiments
• use of genetic knock-outs
• Keep in mind
• Genetic effects are usually complex, involving
  Pleiotropic and Polygenic effects
• Environmental effects are complex involving
  multiple environmental factors
• Complex genetic and environmental effects will be
  further complicated by gene/environment
  interactions.

Taken from Personality and Individual
Differences, Vol. 23, No. 1 (July 1997), pp.
169-180
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Heritability
A measure of how strongly a phenotype is
influenced by genetics Total phenotypic
variationVTVGVEVI where VT total
phenotypic variation observed in a (behavioral)
traitVG variation in population due to
genotypeVE variation in population due to
environmentVI variation in population due to
interaction of VG with VE(i.e. VGxVE)
Heritability (H2) H2VG/(VGVEVI) VG/VT

• Characteristics of H2
• Heritability is standardized variance ranging
  from 0.0-1.0
• Indicates what fraction of the total variance in
  a trait is due to variation in genes
• H20 None of the variance in the trait is
  influenced by genes
• H21 All of the variance in the trait is
  determined by genes

Taken from Personality and Individual
Differences, Vol. 23, No. 1 (July 1997), pp.
169-180
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Philippe Rushton
Primary research interest is altruism and social
learning of generosity
More controversial is on race differences
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Heritability (H2) of IQ 0.70
Average IQ by Ethnic group African Americans
85 Latino 89 White 103 Asian
106 Jewish Americans 115
Correlation between IQ and head/brain size
0.40 (MRI normal adults) 0.24 (MRI clinical
adults)
Taken from Personality and Individual
Differences, Vol. 23, No. 1 (July 1997), pp.
169-180
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Brain size
Brain size and race

• Brain size and SES
• Men
• Unskilled 1,324cc
• Professional 1,468cc
• Women
• Unskilled 1256cc
• Professional 1264cc

• Brain size and sex
• Men 1325g
• Women 1144g
• However no difference in IQ ???

Taken from Personality and Individual
Differences, Vol. 23, No. 1 (July 1997), pp.
169-180
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1 of 6 warbler species that regularly winter in
the British Isles, 4 of which are migratory
Chiffchaff, Blackcap, Firecrest and Goldcrest
winter Atlas 1981-1984, estimates 3,000 Blackcaps
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Quantifying intended flight direction
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