Inbred mice are homozygous, which can lead to severe health problems not found in humans.

“the mouse that we currently have in the lab the typical mice come from mice that were selected for bizarre coat colors and sizes mice that were then inbred for hundreds of generations so that they're absolutely genetically identical to one another and then over the generations of course as we're raising these mice every you know once they started being commercially valuable the companies that produced them would always the ones that left the most young were the ones that formed the next generation so you're always getting this selection for bigger and bigger litters and faster growth and more rapid reproduction”