It is easy to identify both homozygotes and heterozygotes. All plants and animals have them. They are subject to intense natural selection. You can examine many different loci. They are close to the DNA level.
Homozygous cheetahs run faster than heterozygous cheetahs.
The amount of genetic variation in cheetahs is lower than that in other cat species. Skin grafts show that different cheetahs have the same individual recognition proteins on their cell surfaces. Abnormalities in sperm cells could be the result of inbreeding depression. The lack of genetic variation is consistent with one or more population bottlenecks. It has a 3 to 2 advantage in the transmission of gametes.