A variant that occurs when a small group separates from the rest of a population, resulting in increased genetic drift and inbreeding, is called the founder effect.  
Animals that show evidence of this include European bisons and northern elephant seals, and it is thought to have occurred in giant pandas about 43,000 years ago.  Because of this effect, skin grafts from one cheetah to another do not create an immune response.  A variant that occurs when a small group separates from the rest of a population, resulting in increased genetic drift and inbreeding, is called the founder effect.  FTP, name this evolutionary event in which a significant percentage of the population or species is killed or unable to reproduce, resulting in a population reduction of 50% or more.
Animals that show evidence of this include European bisons and northern elephant seals, and it is thought to have occurred in giant pandas about 43,000 years ago.  
bottleneck effect (accept population bottleneck, genetic bottleneck, or variations)