Question

A trait exists in a population of a certain species. The trait has two variations, variation X and variation Y. The percentage of the population that has each variation over several generations are shown in the table below.

Generation 1 Generation 5 Generation 10
Variation X 50% 74% 92%
Variation Y 50% 26% 8%

Which statement correctly describes how and why the occurrence of the variations of the trait changed over time?
A.
Variation X became more common because it increases an individual's probability of surviving and reproducing.
B.
Variation X became less common because it decreases an individual's probability of surviving and reproducing.
C.
Variation Y became less common because it increases an individual's probability of surviving and reproducing.
D.
Variation Y became more common because it decreases an individual's probability of surviving and reproducing.

Answer 1

A. Variation X became more common because it increases an individual's probability of surviving and reproducing.

Explanation: Over generations X's frequency rises (50% → 74% → 92%), so X must confer a fitness advantage, causing individuals with X to survive and reproduce more, increasing its frequency by natural selection.