1. Quantitative genetics

2. Differential survival/reproduction = Evolution
Darwin’s tenets:
Heritable variation +
Differential survival/reproduction =
Evolution
Measuring heritability
-Darwins 2 tenets – heritable variation + differences in survival/reprod success = evol
-imagine popln with continuous variation among indiv in some trait eg. human height
-normally distributed bell curve
-is height heritable?
-what fraction of the variation in height among indiv is due to variation in their genes, and what fraction due to variation in their environment?

3. Heritability = 0
Heritability = 1

4. 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)
-heritability – fraction due to variation in genes
-phenotypic variation = Vp – total variation in a trait
-genetic variation= Vg – variation among indiv due to variation in their genes
-environmental variation=Ve – variation due to environment
-heritability = Vg/Vp = Vg/Vg+Ve
-this is broad sense heritability – degree of genetic determination

5. Broad sense heritability: fraction of the total variation in a trait that is due to variation in genes
Heritability = VP VG
VG + VE =
Phenotypic variation: VP
Genetic variation: VG
Environmental variation: VE

6. Biological parents Foster parents
estimating heritability from parents & offspring
-if variation is due to genes, offspring will resemble their parents
-check by making scatterplot
-2 parents, so use mid-parent value, if 2+ offspring use mid-offspring value
-if no variation due to genes, regression = 0
-if offspring strongly resemble parents, regression = 1
-most traits somewhere between
Biological parents
Foster parents

7. 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)
-variation due to genes & environment
-slope is estimate of heritability
-narrow sense heritability = h^2
VA + VD VG =

8. Genetic variation: VG Phenotypic variation: VP
Narrow sense heritability: a measure of the (additive) genetic variation in a trait
Heritability, h2 = VP VA
VA + VD + VE =
narrow sense vs broad sense heritability
-additive genetic variation = Va – variation among individuals due to additive effects of genes
-dominance genetic variation= Vd – variation among indiv due to gene interactions such as dominance
-total genetic variation = Vg = Va + Vd
-broad sense heritability = Vg/Vp
-narrow sense heritability = h^2 = Va/Vp = Va/Va + Vd + Ve
-almost always mean narrow sense
-recall offspring can resemble parents for reasons other than genes
-eg similar diets, similar exercise regimes etc
-need to ensure no correlation between parental and offspring environs
-could use twin studies if raised apart
Genetic variation: VG Phenotypic variation: VP
Additive variation: VA Environmental variation: VE
Dominance variation: VD

9. Selection differential: difference between the mean of the selected individuals and the mean of the population (S)
measuring differential survival/reprod success
-measuring strength of selectin
-can then combine with heritability to predict evol’ary change in response to selectin
-indiv with some values of a trait survive at higher rates or product more offspring than indiv with other values of a trait
-to measure strength of selection, note who survies and reproduces and who fails to do so
-then quantify the difference between the winners and losers in the trait of interest
-mouse example
-bred indiv with 1/3 longst tails for 18 generations
-measure mean tail length of breeders & of popln
-difference = selection differential =S

11. P: average midparent value for the entire population
Evolutionary response: predicted response of the population to selection (R)
R = h2 S
Slope = h2 = S
O* - O
P* - P R =
predicting evol’ary response to selection
-predicted evolary response to selection = R
R=h^2 S
h^2 = heritability, S = selection differential
P = mean midparent value for entire popln
P* = mean of 10 largest midparent values
P* - P = S, selection differential
O = mean midoffspring values for the entire popln
O* = mean mid offspring value for 10 parents with ihgest midparent vlues
O* - O = R, evol’ary response, if selected 10 largest parents as breeders
Slope = O*-O/P*-P = R/S = h^2
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

12. R S
Slope = h2 =
-so R=h^2 S
-i) can estimate how much of the variation is due to variation in genes
-ii) quantify the strength of selection that results from differences in survival/reprod
-iii) combine these to predict how much of the popln will change from 1 generation to the next