Transcript CH3L2

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
Heritability:
A measure of how strongly a phenotype is influenced by genetics
Total phenotypic variation=VT=VG+VE+VI
where:
VT= total phenotypic variation observed in a (behavioral) trait
VG= variation in population due to genotype
VE =variation in population due to environment
VI = variation in population due to interaction of VG with VE
(i.e. VGxVE)
Heritability (H2)
H2=VG/(VG+VE+VI) = 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:
•H2=0: None of the variance in the trait is influenced
by genes
•H2=1:Taken
All of
the variance in the trait is determined
from Personality and Individual Differences, Vol. 23, No. 1 (July 1997), pp. 169-180
by genes
Philippe Rushton
Primary research interest is altruism and
social learning of generosity
More controversial is on race differences
Rushton
Phillip
Psychology
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3.0
3.1
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
Brain size
Brain size and race
Population
Cubic inches
Cubic centimeters
87
87
86
85
84
83
1427
1427
1410
1394
1378
1361
Mongolians
Modern Caucasians
Native Americans
Malays
Ancient Caucasians
Africans
Brain size and SES
Men
•Unskilled
•Professional
1,324cc
1,468cc
Women
•Unskilled
•Professional
1256cc
1264cc
Brain size and sex
•Men
•Women
***However no difference in IQ ???
1325g
1144g
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