Decline in frequency of allele?

In a large, sexually reproducing population, the frequency of an allele changes from 0.6 to 0.2. From this change, one can most logically assume that, in this environment,





A. the allele is neutral.


B. the allele mutates readily.





C. random processes have changed allelic frequencies.





D. there is no sexual selection.





E. the allele reduces fitness.





I am stuck between B, C, and E but I'm not sure. Please help.

Decline in frequency of allele?
C is correct. Random processes can include major catastrophes like the eruption of Mt. St. Helen's. This is called Genetic Drift. When you have any type of population and a major disaster hits it will change the allelic frequencies. The bottleneck effect or founder effect will occur.
Reply:The question did not mention the drop in frequency was for the following generation. I realize that genetic drift is reserved for small populations but a drastic drop even in a large population would make one think something major happened. I don't think I was completely off base. Report It

Reply:The answer is E. the allele reduces fitness. Fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals. If a genotype has a relative fitness close to one (0.8) it is because natural selection is acting favorably towards the allele because it is beneficial. Therefore, if it has decreased (0.2) then the allele is no longer benefiting members of the population and has ultimately lost fitness.
Reply:Large sexually reproducing population, thus drift is out by itself. In this environment. This indicates no catastrophic occurrences. ATP man may be a good functional biologist, but evolutionarily speaking, he is wrong. E is the only possible answer giver the constraints of the question.
Reply:Yep, E. I don't think it's B. As far as I know, mutation is a pretty random event that usually doesn't favour a particular allele over another. Not saying that it couldn't conceivably happen, but it's not the most logical assumption.





C is probably not the answer they're after because the question says there's a LARGE population. If it were a small population, random events affecting a small number of individuals could easily drastically affect the frequency of an allele, but in a large population, that's less likely to be the case. Not impossible; just less likely.
Reply:I would go with C
Reply:E. the allele reduces fitness.