以生长分化因子9和骨头形态发生蛋白15基因为侯选基因，构建繁殖力不同的5个绵羊品种，这两个基因座位的PCR-SSCP 和PCR-FFLP多态性图谱，阐明这两个基因座位与小尾寒羊高繁殖力的关系。分析不同物种间这两个基因的同源性和进化的保守性。研究成果可为通过标记辅助选择提高绵羊繁殖力提供依据，对育成高繁殖力的“超级羊”具有重要的促进作用。.

Heritability of sheep litter size is pretty low, only around 0.1. Traditional breeding can hardly work to improve litter size. Marker assisted selection (MAS) could improve the efficacy of selective breeding for traits with low heritability by working on selection time, selection strength and accuracy. Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are growth factors secreted by oocytes in growthing ovarian follicles, which are essential for growth and differentiation of early ovarian follicles. Small Tail Han sheep is an excellent domestic sheep breed in China. The lambing percentage averaged 260% in Small Tail Han sheep. GDF9 gene and BMP15 gene were considered as candidate genes for prolific traits. Genetic polymorphisms were analyzed in ewes of Small Tail Han sheep by PCR-SSCP. The relationships between these two genes and high prolificacy in Small Tail Han sheep were analyzed. Fragment amplified by two primers had only two genotypes (AA and AB) in Small Tail Han sheep for GDF9 gene. BB genotype was not detected. Least squares analysis showed that least squares means of litter size in the first parity and the second parity for AA genotype at fragment amplified by primer 1 were 0.30 and 0.77 more than those for AB genotype in Small Tail Han sheep. Least squares means of litter size in the first parity and the second parity were not obviously different between AA genotype and AB genotype at fragment amplified by primer 2(P>0.05). Three kinds of genotypes (AA, AB and BB) were found in Small Tail Han sheep for BMP15 gene. Least squares mean of litter size in the second parity for genotype AA was 0.50 more than that for genotype BB in Small Tail Han sheep. Least squares mean of litter size in the second parity for genotype AB was 0.30 more than that for genotype BB in Small Tail Han sheep. The information found in the present study is very important for improving the reproductive performance in sheep breeds by marker assisted selection.