The three-spined stickleback (Gasterosteus aculeatus) is a species of fish that has both marine and freshwater populations. There are genetic differences between the populations in the different environments. The graph shows the frequency of a certain allele in freshwater and marine populations of stickleback fish. The figure presents a bar graph titled “Frequency of Allele in Two Populations.” The horizontal axis is labeled “Location of Stickleback Population,” and the two categories “Marine” and “Freshwater” are indicated. The vertical axis is labeled “Frequency of Allele,” and the numbers 0 through 1.0, in increments of 0.1, are indicated. The data for each category are as follows. Marine: 0.01 Allele. Freshwater: 0.98 Allele.
In 1978, scientists studied how the fitness of marine sticklebacks would be affected if they were introduced into a freshwater environment. They collected 90 male and 90 female sticklebacks from a marine population and 10 male and 10 female sticklebacks from a freshwater population. The 200 sticklebacks were introduced into a freshwater environment that had no stickleback fish previously.

After the 200 sticklebacks were introduced into the freshwater environment, the scientists collected data on the frequency of the allele in the population from 1978 to 1985. Which of the following best describes the likely results of the scientists’ investigation?

The frequency of the allele continued to be high in approximately 10% of the individuals in the population.

Answer A: The frequency of the allele continued to be high in approximately 10% of the individuals in the population.
A

The frequency of the allele continued to be high in approximately 90% of the individuals in the population.

Answer B: The frequency of the allele continued to be high in approximately 90% of the individuals in the population.
B

The frequency of the allele in the population started very low and continued to increase over time.

Answer C: The frequency of the allele in the population started very low and continued to increase over time.
C

The frequency of the allele in the population started very high and continued to decrease over time.