African cheetahs (Acinonyx jubatus) have extremely low levels of biochemical genetic variation relative to other felids as measured by enzyme electrophoresis, suggesting that interfamilial differences in phenotypic traits may be slight. Quantitative data on the pattern of tail bands collected from both sides of the tails of 64 free-living cheetahs show, however, that individuals differ markedly from each other and that siblings resemble each other significantly more than they do nonsiblings. Furthermore, offspring tail bands show significantly less similarity to the tail bands of their mothers than they do to their siblings. It is argued that environmental factors in utero are responsible for differences in cheetah pelage characteristics in combination with maternal or paternal genetic influences, giving evidence for a degree of phenotypic diversity despite the genetic monomorphism of this species. The analytical techniques developed in this paper are used to show that coalitions of permanently associating male cheetahs are genetically related. These techniques could also be used productively with the many other mammals that have distinctive markings on their bodies and tails.