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Quantitative genetics
Darwin’s tenets:
Heritable variation +
Differential survival/reproduction =
Evolution
Heritability = 0
Heritability = 1
Phenotypic variation: total variation in a trait (VP)
Genetic variation: variation among individuals due to
variation in their genes (VG)
Environmental variation: variation among individuals
due to variation in their environments (VE)
Broad sense heritability: fraction of the total
variation in a trait that is due to variation in genes
Heritability =
VG
VG
=
VP
VG + VE
Phenotypic variation: VP
Genetic variation: VG
Environmental variation: VE
Biological parents
Foster parents
Genetic variation: variation among individuals due to
variation in their genes (VG)
Additive variation: variation among individuals due to
the additive effects of genes (VA)
Dominance variation: variation among individuals due
to gene interactions such as dominance (VD)
VG = VA + VD
Narrow sense heritability: a measure of the (additive)
genetic variation in a trait
Heritability, h2 =
VA
VP
=
VA
VA + VD + VE
Genetic variation: VG
Phenotypic variation: VP
Additive variation: VA
Environmental variation: VE
Dominance variation: VD
Selection differential: difference between the
mean of the selected individuals and the mean of
the population (S)
Evolutionary response: predicted response of the
population to selection (R)
R = h2 S
O* - O
Slope = h2 =
R
=
P* - P
S
P: average midparent value for the entire population
P*: average midparent value for the selected individuals
O: average midoffspring value for the entire population
O*: average midoffspring value for the selected individuals
Slope = h2 =
R
S