[The genetic differentiation of mammalian taxa: their assessment by biochemical genetic markers].

A review of data on genetic differentiation of mammalian taxa has been made on the basis of estimating the percent of fixed gene differences (PFD). The results substantiate the existence of evident differences in the scale of genetic divergence between taxa in different mammalian orders. Among smaller mammals (marsupials, insectivores, chiropterans, myomorph and sciuromorph rodents, african mole rats, and elephant shrews) interspecific differences within a genus involve the average of 25-40% of investigated loci. At the genetic level the value is 50-60%, whereas at the familial level the differences are beyond the resolution capacity of the method (PFD = 60-80%). Orders of larger mammals can be divided into two subgroups. One of them that includes carnivores, artiodactylans, and hystricomorph rodents is characterised by PFD values of 10-14%, 30-50%, and 69-70% at respective levels. The other subgroup composed of proboscideans, primates, pinnipeds, and toothed whales, has a low level of genetic divergence expressed by PFD values of 0-3%, 7-36%, and 50-60% at species, generic and familial levels, respectively. Insufficiency of data on baleen whales and perissodactyls does not allow to cluster them ultimately with any of these groups. There are three possible, but not necessarily alternative, causes for the observed differences in genetic divergence: 1) over-ranking of genera in larger mammals; 2) different paleontological age of orders; 3) unequal rates of molecular evolution.