Inbreeding leads to homozygous MHC alleles. Small populations are forced to engage in inbreeding, and many show signs of inbreeding depression, sometimes to the extent that fecundity is seriously affected. The classic example of a species bottleneck is the cheetah. Cheetahs went through a population bottleneck about 10,000 years ago. They barely escaped extinction and have been hanging by a thread since.
All cheetahs are virtually genetically identical.
They have little genetic variation with which to respond to disease. How conservation biologist cope The major purpose of most zoos is no longer to exhibit animals. They do a lot of work in trying to maintain endangered species.