Which statements about earth's crust are true? check all that apply.
the crust includes soil, rock, and water
there are three different kinds of crust.
the crust is thickest under the ocean.
the ocean crust is made of young rocks
the ocean crust is denser than continental crust.

In the mid-1800s, over-hunting of Northern Elephant Seals reduced their population size to fewer than 40 individuals. However, the population has since rebounded to over 100,000 animals. The population went through a _bottle neck event (genetic drift)_, which makes it more susceptible to _developing a genetic disease_.

Explanation:

Genetic drift is the random change that occurs in the allelic frequency of a population through generations. The magnitude of this change is inversely related to the size of the original population. These changes produced by genetic drift accumulate in time. Eventually, some alleles get lost, while some others might set. Genetic drift affects a population and reduces its size dramatically due to a disaster or pressure-bottleneck effect- or because of a population split -founder effect- . The bottleneck effect most likely affects smaller populations.  

In the exposed example, extensive hunting acted as a pressure that reduced the number of Northern elephant seals to fewer than 100. This population experienced one or many generations of small size since these animals were affected by hunting. As the survivors did not have the whole genetic pool of the original population, the population size might have recovered to a current population size of 100,000 individuals, but the genetic pool might have not. When the small population increases in size, it will have a genetically different composition from the original one. In these situations, there is a reduced genetic variability, with a possibility of developing a peculiar allelic component. If the survivors in the population carried or developed a mutation, probably this mutation passed from generation to generation. It will involve more individuals each time and increase the probability of developing a genetic disease.