Lecture 19 Flashcards Preview

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Flashcards in Lecture 19 Deck (19):
1

F

- Inbreeding co-efficient

2

H

- Heterozygosity

3

N

- Population size, the number of breeding intividuals

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t

- Generation time

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Autozygous (F):

- The probability of that any two randomly chosen alleles in a population are identical by descent
- A1A1 or A2A2 from the same A1 or A2

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Allozygous (1 - F):

- The probability of that any two randomly chosen aleles in a population are NOT identical by descent
- A1A1 or A2A2 from different A1 or A2

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Generational increase in frequency of homozygotes in a selfing population:

- G0 AA 0, Aa 1, aa 0
- G1 AA 1/4, Aa 1/2, aa 1/4
- G2 AA3/8, Aa1/4, aa 2/8
- G AA 1/2, AA 0, aa 0

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Effects of inbreeding:

- Decrease in heterozygosity
- Increase in homozygosity
- Allele frequencies do not change

9

Hardy Weinburg Equilibrium:

- A1A1 = 2pq -2pqF
- p + q = 1

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Homozygous:

A1A1 = p squared (1 - F) + pF

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Heterozygous:

A1A2 = 2pq (1-F)

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Calculating F from observed genotype frequencies:

A1A2 = 2pq (1-F)
- Allele frequency of A1
- Allele frequency of A2
- Observed heterozygosity
- F =

13

Reduction in heterozygosity is a convenient measure of the effect of inbreeding in a population:

- F = (Hexp - Hobs) / Hexp

14

Can we predict how fast F increase and H decrease over time in a finite population?

- Yes
-

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Ft = 1 - [1-1/2N] t the power t (1-Fo)

F = Level of inbreeding in generation t
N = Population size
t = Generation
o = Level of inbreeding in the base population

16

Ht = Ho [1-1/2N] to the power t

Ht = heterozygosity in generation t
Ho = Heterozygosity in the base population
t = generation
N = population size

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From generation t to t+1, there are 2 ways to get alleles IBD

- 1/2N
- Probability of an individual receiving two copies of the same allele (new inbreeding)
OR
- [1-1/2N] Ft
- Probability of an individual receiving copies of two different alleles from generation t, but those alleles are identical by descent from generation t-1 (previous inbreeding)

18

Increase in inbreeding (F) over time in finite populations:

Ft = 1 [1 - 1/2N]to the power t
- F will increase over time as a function of population size (N)
- When N is large, F increases slowly over time
- When N is small, F increases rapidly over time

19

Decrease in heterozygosity over time in finite populations:

Ht = Ho [1-1/2N] to the power t
- H will decrease over time as a function of population size (N)
- When N is large, H decrease slowly over time
- When N is small, H decreased rapidly over time