Is genetic drift necessarily deleterious? I read that genetic drift is random variation in the relative allele frequencies of a population. !enter image description here This question however seems to pin genetic drift down to increasing deleterious allele frequencies. Is the answer to this question correct? I don't think that increase of a deleterious allele necessarily indicates that genetic drift is operating; it suggests genetic drift, because one would think that such alleles should decrease in frequency rather than increase, but random chance in a large population can also increase the frequency of deleterious alleles.

Drift is a random element of evolution from one generation to the next, it is equally likely to spread a deleterious mutation as a beneficial one.

The reason the answer is D is because selection should remove a deleterious allele, while drift makes no distinction, and is therefore the only scenario where drift is expected to be a reasonable answer. However, it is possible for drift to contribute to all of those scenarios.