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?
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