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.

Question

Quizplus · Accepted Answer

The fact that the proportion of plants with notched leaves is increasing over many generations indicates that there is some selective advantage to this trait. It is possible that the notched leaves help the plant collect more sunlight or resist pests. Directional selection, where individuals with a certain trait have a higher fitness, would cause the frequency of the allele for notched leaves to increase over time.

In a Large Population of Plants, Notches in the Leaves