Which scenario is most likely to maintain trait variation in

Which scenario is most likely to maintain trait variation in a population over time?

Female fish prefer to mate with males who have whatever color allele is rare in a population at any given time

There is strong positive selection on an uncommon, recessive allele

There is weak positive selection on a common, dominant allele

A population of crickets is small and isolated (please explain reasoning)

Solution

Answer is (b) There is strong positive selection on an uncommon, recessive allele.

Because when there is a strong positive selection on any trait, it will appear prominently in that population in future generations, even when it is recessive.

Female fish prfers to mate only with males who are rare in that population, so it will not lead to random mating as the mate will not be present for mating each time.

When there is weak positive selection on a common, dominant allele, It may get lost due to natural selection after many generation or can be less active in participation for genetic recombination.

Population of crickets when isolated and small, will not be able to result into higher degree of variation in allele frequency over time. Because in isolated population, there are same alleles mating together having no other choice. It will also result into errors and mutations like polyploidy. And because the population is very small, it may not be possible for each allele to survive natural selection.