Lecture 6 -Phenotypic Evolution Flashcards
What does the selection gradient measure?
strength of directional selection on a quantitative trait
How does the selection gradient measure the strength of directional selection?
measures the trait of interest and the fitness for a set of individuals who vary in the trait of interest
When beta is positive, what does this say about the strength of directional selection?
directional selection favors larger values of the trait
When beta is negative, what does this say about the strength of directional selection?
selection favors smaller values of the trait
When beta is 0, what does this say about the strength of directional selection?
there is no directional selection acting
What values of selection gradient indicate a moderately strong directional selection?
-0.5 and 0.5
What value of selection gradient indicates a strong directional selection?
1
How can we predict the amt of evolutionary change given directional selection?
by calculating the difference btw mean of a trait at the start of generation and the mean of trait now
What does the Breeder’s equation predict?
amt of evolutionary change that results from selective breeding
What is breeders equation formula?
delta z = change in the mean of the trait
delta z = (mean of trait in present generation)- (mean of trait in next generation) = (selection differential)(heritability)^2
What does h^2=0 mean?
no resemblance between parents and offspring
What does it mean if h^2=1?
parents and offspring are identical
What does it mean if heritability shows a positive slope?
trait is heritable between parents and offspring
What happens when S=0?
no change in the mean of the trait and thus no evolutionary change
What does h^2 indicate?
heritability = slope of regression line of a mean value trait from two parents and the value of trait in their offspring
What 4 things does gene expression depend on?
age, tissue type, interactions among gene loci, and direct environmental influence
What is the Nature vs Nurture equation?
Vp = Vg + Ve
Vp = overall phenotypic variance
Vg = genetic variance (phenotypic variation caused by genetic variation)
Ve = environmental variance components
How does human height represent nature vs nurture?
height is strongly heritable but is influenced by diet
Why do we partition phenotypic variation into genetic and environmental components?
- distinguishes role of heredity vs environment
- genetic variance is determined by genetic interactions within individuals averaged over the population
What is the equation for variance of genetic components of Vg?
Vg = Va + Vd + Vi
Va = additive genetic variance
Vd = dominance variance
Vi = epistatic interactions of alleles at different loci
What is additive genetic variance?
avg effect of substituting one allele for another
What is the only kind of genetic variance that contributes directly to evolutionary change?
additive genetic variance
What is dominance variance?
variance due to dominance of alleles at the same locus
Why doesn’t dominance variance contribute to evolutionary change?
bc heterozygotes aren’t intermediates in a dominance situation, they exhibit phenotype of dominant allele
What is epistatic variance?
variance due to epistatic interactions of alleles at diff loci where the effect of one allele depends on second allele
What can environmental fluctuation maintain?
variation and heritability
What does melanocortin receptor-1 do ?
protein produced by the MC1r gene that regulates production of melanin (dark pigment) in hair, feathers and scales
What is the main cause for melanin polymorphism?
a few amino acid substitutions
