Study On Estrogen Receptor As A Candidate Gene For Prolificacy Of Small Tail Han Sheep

Due to the functions that estrogens play in the regulation of reproduction, development of the mammary gland, growth and Differentiation of cells, estrogen receptors and their genes are considered candidates for the markers of high fecundity traits in sheep. Based on the genetic polymorphism of ESR gene , we try to link this candidate gene with the high productivity of Small Tail Han sheep, to futher provide scientific evidence for the basic genetic reseach on Small Tail Han sheep high productivity.In this research single nucleotide polymorphism of exon 1 of estrogen receptor (ESI?) gene was detected in 5 sheep breeds (high fecundity : Small Tail Han sheep, Hu sheep and German Mutton Merino sheep , low fecundity: Dorset sheep, Suffolk sheep) and 5 goat breeds (high fecundity : Jining Grey goats, medium fecundity: Wendeng Dairy Goat, Boer does, low fecundity : Liaoning fuzz goat, Beijing Native Goat) by PCR-SSCP. The results indicated that there were three genotypes (AA, AB and BB) in Small Tail Han sheep, Hu sheep and German Mutton Merino sheep. Two genotypes (AA, AB) were detected in Dorset sheep and Suffolk sheep. There were one genotypes (AA) in five goat breeds.The sequencing results showed that there was a mutation (C→G) at 363bp of exon 1 of ESR gene in BB genotype compared to AA genotype. There were 10 mutation at partial exon 1 of ESR gene in small tail han sheep compared to sequence of exon 1 of ESR gene in sheep publicized by GenBank (X98010), and inserted three C between 324bp and 325bp of exon 1 of ESR gene. The Statistic results showed that in Hu sheep, German Mutton Merino sheep, Small Tail Han sheep, Suffolk sheep and Dorset sheep, frequency of A allele were 0.672, 0.786, 0.846, 0.857and 0.867 respectively, frequency of B allele was 0.328, 0.214, 0.154, 0.143, and 0.133 respectively. X~2 fitness test showed that fragments amplified by two primers were in a state of Hardy-weinberg Equilibrium. The genotype distribution was significantly different (P<0.01) between Small Tail Han sheep and Hu sheep. The genotype distribution was different (P<0.05) between Dorset sheep and Hu sheep. The genotype distribution had no difference between other sheep breeds.From Small Tail Han sheep with littering records, least squares analysis showed that the ewes with genotype AB and BB had 0.51 (P<0.05)and 0. 7 (R0. 05) lambs more than those with genotype AA in Small Tail Han sheep, respectively. These results showed that the estrogen receptor locus is associated with a major gene influencing prolificacy in Small Tail Han sheep. In view of our results, marker-assisted selection using ESR is warranted to increase litter size in sheep and will be of considerable economic value to mutton producers.