The Devil's Hole Pupfish is an endangered species native to North America. The entire population of 263 fish live in the same cave in Nevada. Researches from the University of California- Berkeley, while studying a sample of Pupfish, including 8 Devil's Hole Pupfish, have determined that the Devil's Hole Pupfish is so inbred that 58% of genes in the 8 pupfish that were studied are entirely identical. Since high levels of inbreeding lead to lower biological fitness, it is assumed this is one of the reasons that the species is endangered. In addition to this, researches have found that 15 genes have disappeared entirely from the genome.
Of course, some of these issues can also be due to the fact that this particular pupfish lives in 93 degree water, with low oxygen and a very low supply of food. Some of the genes seem to have been deleted due to this, and it can also be why they are endangered. I would love to see the results of the gene overlap in a larger sample of Devil's Hole Pupfish in the future.