Question

In a large population of plants, notches in the leaves are caused by a dominant allele N and lack of notches by a recessive allele n. Over many generations the proportion of plants in the population with notched leaves increases. What is the most likely cause?A) Dominant alleles generally increase in frequency over time.B) The recessive alleles were all masked by the dominant alleles.C) Directional selection favored plants with notched leaves.D) Genetic drift caused a steady movement toward a greater proportion of plants with notched leaves.

Answer 1

Answer:

C

Explanation:

If the population is in equilibrium, the allele frequencies will be constant.

There is nothing about the heritability of dominant or recessive alleles that make dominant ones any more likely by nature. This rules out choices A and B.

Genetic drift mentioned in D refers to alleles leaving a population. Nothing like this was mentioned in the question, so count that answer out.

C is the only remaining answer by process of elimination. It is also the most logical choice. Directional selection refers to a process of natural selection wherein extreme phenotypes (notched leaves, or non-notched leaves) are favored. In this case, there may be some external pressure causing notched leaf plants to be more evolutionarily fit, meaning that they survive long enough to reproduce more and increase allele frequency of the dominant allele.