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?

Environmental hypothesis

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 (VT=VE)•cross-fostering experiments & twin studies

•Hold environment constant & explore effects of genes alone (VT=VG)•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

A measure of how strongly a phenotype is influenced by geneticsTotal phenotypic variation=VT=VG+VE+VI

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:

Heritability (H2)

H2=VG/(VG+VE+VI) = VG/VT

Characteristics of H2Heritability is standardized variance ranging from 0.0-1.0Indicates what fraction of the total variance in a trait is due to variation in genes:

•H2=0: None of the variance in the trait is influenced by genes•H2=1: 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

Rushton Phillip  Psychology 1/19/05

14 3.0 3.1

Primary research interest is altruism and social learning of generosity

More controversial is on race differences

Philippe Rushton

Heritability (H2) of IQ = 0.70

Average IQ by Ethnic group:African Americans 85Latino 89White 103Asian 106Jewish 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

Population Cubic inches Cubic centimeters Mongolians 87 1427 Modern Caucasians 87 1427 Native Americans 86 1410 Malays 85 1394 Ancient Caucasians 84 1378 Africans 83 1361

Brain size and race

Brain size and SESMen

•Unskilled 1,324cc •Professional 1,468cc

Women•Unskilled 1256cc•Professional 1264cc

Brain size and sex•Men 1325g•Women 1144g

***However no difference in IQ ???

Brain size

Taken from Personality and Individual Differences, Vol. 23, No. 1 (July 1997), pp. 169-180

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

Quantifying intended flight direction