Flashcards in Lecture 11 - Population Genetic Structure Deck (20)
What processes affect differentiation?
-Gene flow reduces differentiation
-Genetic drift increases differentiation
-Selection could either:
Different selection pressures - increase
Universally adaptive genes - decrease
How can we measure differentation?
The fixation index
What is the Wahlund effect?
A subdivided population has fewer heterozygotes than expected from the overall population
What is genetic differentiation?
-Reduction in heterozygosity due to subpopulation divergence
Ht = expected heterozygosity (He) from the overall p and q in the total population
Hsbar = average expected heteroxygosity from each of the sub populations
How does inbreeding affect heterozygosity?
Inbreeding leads to a reduction in heterozygosity
What is the inbreeding coefficient?
-Average difference between observed and expected heterozygosity due to non-random mating
Hi = average observed heterozygosity
Hsbar = average expected He across each of the sub populations
-Can be positive (deficit of heterozygotes) or negative (excess of heterozygotes)
What is the overall inbreeding coefficient?
-Includes inbreeding and population divergence
HT = expected heterozygosity from the overall p and q in the total population
Hi: average observed heterozygosity
-can be positive (deficit of heterozygotes) of negative (excess of heterozygotes)
What equation relates Genetic differentiation to the Inbreeding coefficient?
Overall inbreeding coefficient
1 - Fit = (1 - Fis)(1 - Fst)
What do you know about population divergence when Fst = 0?
No population divergence
-all allele frequencies are the same
What do you know about population divergence when Fst > 0?
There is population divergence
-allele frequencies differ
What do you know about the status of inbreeding when the actual heterozygosity is less than the expected heterozygosity, and Fis > 0?
Evidence for inbreeding
-reduction in heterozygosity
What do you know about the status of inbreeding when the expected heterozygosity is equal to the actual, Fis = 0?
No evidence for inbreeding
What are the features of isolation by distance?
There is greater differentiation between populations that are further away from each other due to less dispersal and gene flow
What is the formula for the estimation of number of migrants per generation?
Wright's F statistics, 1931
Fst = 1/(4*Ne*m + 1)
Ne = effective population size
m = migration rate
What are the limitations of Wright's f-statistics for estimating the number of migrants per generation?
Makes a number of unrealistic assumptions
-all populations are identical (with equal numbers of emigrants)
-no spacial structure
-populations are at equilibrium
What are the features of the lake Erie garter snakes (selection)?
Melanistic forms unusually common near lake Erie
-selection for thermoregulation may outweigh selection for crypsis
Colour pattern is a one locus, two allele trait
-melanistic is recessive to striped
Morph frequencies highly variable amongst sites
-there may be an element of drift influencing colour pattern
Higher Fst (genetic differentiation) expected at loci under divergent selection compared to neutral or universally adaptive traits
How is Fst expected at loci under divergent selection compared to neutral or universally adaptive traits?
Higher Fst expected at loci under divergent selection
-compared to neutral or universally adaptive traits
What are Wright's three F-statistics?
Genetic differentiation (Fst)
Inbreeding coefficient (Fis)
Overall inbreeding coefficient (Fit)
Which of Wright's three F-statistics are the most important?
Genetic differentiation (Fst)