The fur color in a species of rodent is controlled by a gene with only two alleles. In a generation of these rodents, there 240 individuals, and the frequency of the dominant allele is 0.83. After four generations, the dominant allele frequency in a population of 300 individuals is 0.72. Which of the following is most likely true of the dominant allele?

I found the whole exercise on the internet. Here are the options:

"A. It is becoming more difficult for the dominant allele to mask the recessive allele.

B. It is beneficial to the species because it results in an increase in population over time.

C. It results in a phenotype that provides less of a survival advantage than the recessive phenotype.

D. It will become recessive and eventually disappear after several more generations. "

Correct answer: C.

The fact that after four generations (which is quite many to only have an increase of 60 individuals in the total population) there was a decrease in about 11% of the frequency of the dominant allele, it shows that the dominant allele results in a phenotype that provides less of a survival advantage than the recessive phenotype. Both alleles tend to be in equal frequency over time when there is no selection pressure. The fact that the frequency of the dominant allele was so high and is getting lower comes to show that it was probably an important allele for survival, but also that is not as much anymore and is most likely becoming less advantageous for survival purposes - which explains also why there isn't a greater increase in population over the generations.