Question

1. Fixation of Dominant Alleles Start with a population that has a gene with two alleles (A and a) with classical Mendelian dominance that are at equal frequency (p0.5. q 0.5). Assume this first generation is at hardy Weinberg equilibrium. Calculate the genotype frequencies AA- a. Aa b. Now assume some environmental change that makes the recessive phenotype completely unfit (fitness- 0). Calculate the allele frequencies and genotype frequencies in the second generation. (Hint: Your calculations might be easier if you assume a population size of 100) Aa- What was the reduction in the fre quency of the recessive allele from generation #1 to generation #2? Assuming the same fitness for the recessive phenotype, calculate the allele frequencies and genotype frequencies in the third generation. c. Aa- What was the reduction in the frequency of the recessive allele from generation #2 to generation #3? d. There a difference in the change in allele frequencies between generations even though the level of selection remained the same. Why! What type of selection is this and what would happen if we continued this process over many generations? e.

Answer 1

Hardy Weinberg equilibrium is a fundamental model of population genetics that explains the distribution of genotype frequency in the species pool. The principle states that in the absence of evolution, the genotypic frequency of a population will remain constant from generation to generation.

a. As the population have two alleles with classical Mendelian dominance at allele frequency p = 0.5 and q = 0.5, the frequency of genotypes will be,

AA = 0.25

Aa = 0.5

aa = 0.25

b. In the case of unfit (fitness = 0) recessive phenotypes, the genotype frequency will be,

AA = 0.25

Aa = 0.5

aa = 0

and phenotype frequency will be,

q = = 0

frequency(aa)

p = 1 - q = 1 - 0 = 1

The reduction in the recessive allele from generation #1 to generation #2 is 100%.