A population consisting of 1,000 individuals is reduced to a single female and a

Question

A population consisting of 1,000 individuals is reduced to a single female and a single male. The population then doubles in size each generation until it reaches its former size.

1.) What proportion of heterozygosity in the original population would you expect to be lost because of this bottleneck?

2.) If we eliminate variability in reproductive success we can nearly double the effective population size. Why is it impossible in random mating population to eliminate Mendelian segregation so that we could further increase effective population size? That is, couldn't we just screen all the progeny at a particular locus to insure that the numbers of alleles in the progeny are the same as in the parental generation? There is at least one way to eliminate Medelian segregation, although it has other serious drawbacks. Can you describe such a way?

Explanation / Answer

Here the population is undergoing a severe bottleneck, say N1=1000, N2=2 (single female and single male) N3=2N2 (2X2=4)...........Then it reaches its former size Nt = 1000 (where N= No.of individuals in each generation)

1) The rate of loss of heterozygosity is I /2N.

Proportion of the heterozygosity lost in generation N1 is 1/(2x1000)=1/2000=0.0005=0.05%

Proportion of heterozygosity lost in generation N2 is 1/(2X2)=1/4=0.25=25%

Proportion of heterozygosity lost in generation N3is 1/(2X4)=1/8=0.125=12.5%

2) Two sources which contribute to genetic drift are reproductive differences and Mendelian segregation. These two sources contribute equal to the genetic drift.Thus eliminating the first source will double the effective population size. Unfortunately there is no way to eliminate the second source.

In random mating population its is impossible to eliminate the Mendelian segregation. In random mating population there is a mixing all the sperms ad the eggs in the population together. Therefore the allelic frequency doesn't chage, thus the proportions of homozygotes and heterozygotes in each successive generation will remain the same. Non-sexual reproduction (cloning etc.) is the one way to eliminate the Mendelian segregation.

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