The Northern elephant seal went through a severe population decline as a result of hunting in the late 1800s. The population has rebounded but is now homozygous for nearly every gene studied. This is an example of:
A) negative assortive mating
B) migration
C) mutation
D) a bottleneck
E) disruptive selection

Explanation:            

Northern elephant seal is an example of bottleneck effect

In bottleneck effect the elimination of inferior genotype from a homogeneous gene pool occurs due to the strong natural selection pressure and changing environmental conditions which leads to the genetic drift and only a few most adapted genotype survives and flourish

In case of Northern elephant seal, due to hunting a population decline occurred, environmental conditions changed as a result few genotypes homozygous for every gene is present

what's the