Question

5. Tay-Sach disease is due to an autosomal recessive allele t. The disease results in death of tt individuals before reproductive age. The relative fitnesses of the genotypes are TT=1, Tt=1, tt=0.

a. What type of selection is occurring on this locus, and what do you expect will happen to the f(t) over time?

b. Explain in general terms how Mutation-Selection Balance can keep the t allele in the population at a constant (equilibrium) frequency.

Answer 1

Negative selection is occurring at this locus that is trying to remove the deleterious alleles from the population. If this continues, f(t) will reduce rapidly over generations and tend to become zero.

Mutation-selection balance counteracts the negative selection. It maintains all the different alleles in a population. Although negative selection tends to remove the deleterious allele, mutation-selection balance maintains the allele in population by mutating a wild-type allele.