Final answer:
The necessary mutation rate to maintain the frequency of the recessive allele e at 0.001 in the pig frog population by mutation-selection balance, given the relative fitness of ee individuals is 0.2, is 0.0000008. Therefore, option 3 is the mentioned correct option in the final answer.
Step-by-step explanation:
The question involves understanding the genetic concept of mutation-selection balance, which predicts the frequency of an allele in a population considering the mutation rate and selection against it.
The allele frequency is maintained at 0.001 in the pig frog population despite the fact that individuals with genotype ee, who have a lower fitness, are subject to natural selection. Since the question states that the fitness of ee individuals is 0.2 relative to the fitness of 1 for the other genotypes, and we aim to maintain the allele frequency of e at 0.001, we can use these values to calculate the mutation rate necessary to maintain this equilibrium.
Assuming mutation is the only source replenishing the frequency of e diminished by selection, and given the large population size, the mutation rate m can be approximated by the product of the allele frequency q (0.001) and the relative fitness reduction in ee individuals (1 - 0.2 = 0.8). The mutation rate can thus be calculated as m = q * (1 - relative fitness of ee), which equals 0.001 * 0.8 = 0.0008. Therefore, the necessary mutation rate to maintain the allele frequency by mutation-selection balance is 0.0000008.