ffecient of relatedness and predictions of complex genetic influenc 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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Coeffecient of relatedness and predictions of complex genetic influences
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 - PowerPoint PPT Presentation
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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