A. Assume 2 loci, each with allele frequency .5, the population is subdivided, a

Question

A. Assume 2 loci, each with allele frequency .5, the population is subdivided, and allowed to mate at random within each. But due to limited effective population size, each population becomes 100% inbred.

What are the expected genotypic frequencies of each locus in each population given the initial frequencies and level of inbreeding? Because each locus drifts independently there are 4 possible combinations of genotypic frequencies between lines.

For each of those 4 possible parent line combinations, cross the populations. What are the expected frequencies of genotypes among the F1 offspring.

What are the expected mean phenotypes of the parents and the F1given the Dominance model above .

From these examples, which combinations gave an F1 greater than the mean of the parents and which gave an F1 greater than either parent?

Heterosis Dominance What is the basis for? Over-dominance model Model Over-dominance? AA-40 BB-20 AA-40 Aa-40 Bb-20 Simple Dominance Aa-60 aa-0 bb-0 Aa 20 Parent 1 Parent 2 20 40 AA aa F1 60 AaBb

Explanation / Answer

Basis of over-dominance model: (Please note: there should be a misprinting in writing 'aa' as 'Aa' for the value of 20).

The over-dominance model states that the frequency of heterozygous population will be more than homozygous population.

Dominance model: This is a relationship between alleles of a gene. And is not related to two genes; 'A' and 'B' in this case. Out of the two alleles one will be dominant, represented by capital letter ('A' and 'B' in this case) and the other will be recessive, represented by small letter ('a' and 'b' in this case).

100% inbreeding means the two loci are identical or there is equal chance of passing each locus to the next generation. Inbreeding coefficient = 1

Each loci has allele frequency 0.5 = frequency of locus 'A/B'= frequency of locus 'a/b'. A and B are same

New genotype frequency = old genotype frequency * inbreeding coefficient

So, genotype frequency of 'AA' = 0.5*0.5*1 = 0.25

Genotype frequency of 'aa' = 05*0.5*1 = 0.25

Genotype frequency of 'Aa' = 2*0.5*0.5*1 = 0.50

Suppose 'A' and 'B' locus drifted independently, then the number of possible combination of genotype frequencies come out to be more than 4. I think there is a misprint here. So, please check the same and resend

AB, Ab, aB, ab will combine together to give 16 genotypes; not four. Phenotypes will be four.

According to dominance model, all F1 will be “AaBb”. F2 will have four phenotypes in the ration 9:3:3:1.

**From these examples, which combinations gave an F1 greater than the mean of the parents and which gave an F1 greater than either parent? For this part you have to clarify whether it is four phenotypes or four genotypes.

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