if any environmental or human activity leads to a drastic decline in the population of individuals then such an event is known as a population bottleneck.
In the case of bison, overhunting (human activity) led to a bottleneck event.
Overhunting decreased the population of bison to such an extent that it faced the threat of extinction, however, due to regulations its population has recovered.
However, since the new population recovers from a small group of individuals left due to the bottleneck effect, the genetic variability is greatly reduced.
Explanation: since the gene controlling the white eye is recessive Gene its not expressed even in the offspring hence we have 2 red eyes male and 2 red eye female.
