Lecture 11 - Population Genetic Structure Flashcards Preview

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Flashcards in Lecture 11 - Population Genetic Structure Deck (20)
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1

What processes affect differentiation?

-Gene flow reduces differentiation
-Genetic drift increases differentiation
-Selection could either:
Different selection pressures - increase
Universally adaptive genes - decrease

2

How can we measure differentation?

The fixation index

3

What is the Wahlund effect?

A subdivided population has fewer heterozygotes than expected from the overall population

4

What is genetic differentiation?

Fst
-Reduction in heterozygosity due to subpopulation divergence

Where:
Ht = expected heterozygosity (He) from the overall p and q in the total population
Hsbar = average expected heteroxygosity from each of the sub populations

-always positive

5

How does inbreeding affect heterozygosity?

Inbreeding leads to a reduction in heterozygosity

6

What is the inbreeding coefficient?

Fis
-Average difference between observed and expected heterozygosity due to non-random mating

Where:
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)

7

What is the overall inbreeding coefficient?

-Includes inbreeding and population divergence

Where:
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)

8

What equation relates Genetic differentiation to the Inbreeding coefficient?

Overall inbreeding coefficient
1 - Fit = (1 - Fis)(1 - Fst)

9

What do you know about population divergence when Fst = 0?

No population divergence
-all allele frequencies are the same

10

What do you know about population divergence when Fst > 0?

There is population divergence
-allele frequencies differ

11

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

12

What do you know about the status of inbreeding when the expected heterozygosity is equal to the actual, Fis = 0?

No evidence for inbreeding

13

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

14

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

15

What are the limitations of Wright's f-statistics for estimating the number of migrants per generation?

Makes a number of unrealistic assumptions
-no selection
-no mutation
-all populations are identical (with equal numbers of emigrants)
-no spacial structure
-populations are at equilibrium

16

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

17

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

18

What are Wright's three F-statistics?

Genetic differentiation (Fst)
Inbreeding coefficient (Fis)
Overall inbreeding coefficient (Fit)

19

Which of Wright's three F-statistics are the most important?

Genetic differentiation (Fst)

20

What can Genetic differentiation (Fst) be used to asses?

-population structure (i.e. is most genetic variation between or within populations)
-migration rates (but with caution)
-selection (which loci, and what kind of selection)