G-band patterns of the Siberian snow sheep (Ovis nivicola) and their relationship to chromosomal evolution in sheep.

G-band patterns of the Siberian snow sheep, Ovis nivicola alleni, 2n=52, were compared with the patterns reported in 2n=54 wild Asiatic mouflon and 2n=54 North American sheep and those in domestic sheep with 2n=54, 53, and 52. The three largest pairs of biarmed autosomes displayed indistinguishable, presumably homologous, G-banding patterns in all types of sheep. The banding and morphology of the fourth pair of biarmed autosomes in O.nivicola differed from those of the three translocation variants described in domestic sheep. Wild sheep with 2n=54 may have evolved monophyletically from an ancestral 2n=58-56-54 population or polyphyletically by a series of independent, nonrandom fusions. In contrast, the fouth pair of biarmed autosomes in O.nivicola and in 2n=52 domestic sheep variants may have resulted from random fusions of different chromosomes.