Final answer:
The frequency of a slightly deleterious allele at equilibrium due to mutation-selection balance is expected to be higher in a population with weak selection against it, as weaker selection allows the allele to persist despite being slightly harmful.
Step-by-step explanation:
The frequency of a slightly deleterious allele maintained at an equilibrium frequency by mutation-selection balance would be higher in a population with weak selection against the allele. This is because weak selection pressure allows the allele to persist in the population despite its slightly negative effects on fitness. Conversely, strong selection would more efficiently remove such alleles from the gene pool. High mutation rates could introduce the allele more frequently, but the overall equilibrium frequency would largely depend on the interplay between how often the alleles are produced by mutation and how quickly they are removed by selection.
Natural selection, mutation-selection balance, and allele frequency are all important concepts in population genetics, which is the study of how selective forces change allele frequencies in a population over time. Mutation is the ultimate source of genetic variation in populations, introducing new alleles that may be either beneficial, harmful, or neutral. The dynamics of these mutations and the selective forces acting upon them govern the composition of a population's gene pool.