Abstract: Using the method of " random sampling in typical colonies of the central area of the habitat " and several electrophoresis techniques, the variations of 17 structural loci encoding blood proteins in 60 Small Tailed Han sheep and 73 Tan sheep were examined and compared with those of 14 other sheep populations in China and other countries to explore their levels of genetic differentiation. The average heterozygosity of Small Tailed Han sheep and Tan sheep was 0.2360 and 0.2587, respectively. The average polymorphic information content valued 0.1974 and 0.2102, respectively. The average effective numbers of alleles were 1.5723 and 1.5751, respectively. The coefficients of gene differentiation in four groups (including 4, 6, 13, 16 sheep populations, respectively) were 0.049323, 0.059987, 0.1728 and 0.201256, respectively, indicating that the degree of gene differentiation at structural loci in Hu sheep, Tong sheep, Small Tailed Han sheep and Tan sheep was least, that in above-mentioned four sheep populations and two Mongolian sheep populations was the second, and that in sheep populations belonging to Mongolian sheep group, South Asian sheep and European sheep was the highest. The earlier researchers' conclusions that Small Tailed Han sheep and Tan sheep both evolved from Mongolian sheep was further verified by the results in this study. Hu sheep, Tong sheep, Small Tailed Han sheep and Tan sheep were decreasingly affected by the bloodline of Mongolian sheep. The relationships among sheep populations were not closely related to the distances among sheep populations.

Key words: Small Tailed Han sheep, Tan sheep, Structural loci, Genetic differentiation