A zygote is immediately formed after fertilization between two gametes. This cell is eukaryotic and made up of a combination of the DNA in both gamete. Zygote contains all the hereditary information essential in the formation of a new individual.
The correct answer to this question is this one: a.) bottleneck effect. Increased poaching nearly led to the extinction of the American bison. The kind of effect that does this example represent is called the bottleneck effect. Hope this helps answer your question.