There are two populations of trout in a town, both of which inhabit a different lake. These lakes are connected by a stream, and trout from these two populations are able to breed with one another. This is an example of which of the following?
a. gene flow.
b. genetic drift.
c. the bottleneck effect.
d. the founder effect.
e. None of the answer options is correct.

In population genetics, gene flow is the exchange of alleles between individuals from two populations. This exchange generates genetic variation because a population can acquire alleles that were not present in its genetic pool before the genetic flow.

In this example there are two different trout populations. Each population lives in a different lake, however these lakes are connected and therefore the genetic flow -that occurs through the reproduction of individuals from different populations- is possible.