3. A population of salmon lives in Canada and has a heterozygosity of 90% and 10

Question

3. A population of salmon lives in Canada and has a heterozygosity of 90% and 10 equal-frequency alleles at a single autosomal locus. A small group of 10 fish from this population colonize a remote river in Patagonia, Argentina after an aspiring angler introduces them. The population stays at 10 fish.

a. In how many generations will the expected heterozygosity in Argentina reach 70%?

   b. In how many generations do we expect the number of alleles to fall to 8? Assume the alleles remain at equal frequencies (though not at 10% each).

Explanation / Answer

Allele frequency is the proportion of all alleles at a single locus that is of a specified type. Allele frequency change over time.

Heterozygosity is the proportion of individuals heterozygous( as opposed to homozygous) for alternate alleles at a specific locus.

a. Alleles rarely undergo mutation in a single generation so are stable in their next generation.According to Hardy-Weinberg's principle allele frequency remains constant from generation to generation unless some external force is applied. In this case, the external force is the change of habitat.Migration of population is normally ignored in Hardy's principle. Hence the population heterozygosity will reach 70% only if there is a genotype(change in genes) at some stage after the first generation offsprings are born.

B. The number of alleles may fall to 8 even if alleles frequencies remain the same when the balancing selection depends on the environment for the fitness of the homozygous genotype. If the population of 10 salmons remain in the same river in Argentina there will definitely occur some deaths due to degeneration of traits and the number of alleles will fall.

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