16_Quantitative_Genetics_II.pdf - FRSC-BIOL 3700 16 – Quantitative Genetics II Aaron Shafer Last Lecture • The model P = Xm Xp ε Last Lecture ●

16_Quantitative_Genetics_II.pdf - FRSC-BIOL 3700 16 –...

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FRSC-BIOL 3700 16 – Quantitative Genetics II Aaron Shafer
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Last Lecture The model P = X m + X p + ε
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Last Lecture The additive model: V P = V A + V E , where: Var { X m } = Var { X p } = V A /2 h 2 = V A = V A V P V A + V E
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Last Lecture Predicting phenotypes of relatives
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The response to selection R = h 2 S is known as the breeder’s equation where: R = known as the selection response, the change in means across a generation (i.e. the average expected value of the offspring) h 2 = heritability S = known as the selection differential, which is the change in means within a generation due to selection
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Response to selection = trait evolution S R
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The response to selection If there is no change across generations ( R = 0 ) – what is the heritability? Likewise, if we selected individuals that on average were 2 inches taller than the mean ( S ), what is the selection response assuming 80% heritability ?
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Selection for nest building behaviour Mice differ in the amount of cotton they incorporate into nest – question becomes is this genetic? Use an artificial selection experiment to measure S in mice; each generation select individuasl that incorporate a lot of cotton and a little bit of cotton into their nest (+ control); allow them to reproduce in the next generation
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Selection for nest building behaviour
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h 2 from inbred strains We have looked at using relatives, but another common approach is to use inbred strains Inbreeding leads to genetic uniformity (standarized genetic background, EXCEPT possibly at loci of interest) V F1 = variation within an inbred strain or among the F1 progeny V F2 = variation among F2 progeny H 2 “broad sense” = (V F2 - V F1 ) / V F2
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Avoidance learning by inbred strains
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As discussed last lecture : life history traits tend to have low heritability, presumably because selection reduces genetic variation, but almost all traits have some heritable variation Heritabilities in Drosophila
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Influence of the environment: h 2 = V A / V A + V E
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Correlated response to selection Selected for (increased and decreased) flight time in milkweed bugs Wing length is associated with differences in migratory behavior in this insect If there are genetic correlations between the
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