Abstract: Single nucleotide polymorphism in DNAbinding domain and ligandbinding domain of the progesterone receptor (PGR) gene was detected in both high prolificacy sheep breeds (Small Tail Han and Hu sheep) and low prolificacy sheep breeds (Dorset and Texel sheep) with three pairs of primers by polymerase chain reaction (PCR)single strand conformation polymorphism (SSCP). No polymorphism was detected in the amplified regions in the four sheep breeds tested. DNA fragments of exons 5, 6 and 9 of PGR gene in Small Tail Han sheep were cloned into pGEMT Easy vectors and the nucleotide sequences were detected. Comparing the partial sequences of sheep PGR gene from GenBank, the complete sequences of DNAbinding domain and ligandbinding domain of sheep PGR gene were obtained and the amino acid sequences of the two domains were deduced. The comparison of the two domains of PGR gene in human, rabbit, dog, sheep, rat and mouse showed that the homologies of the nucleotide sequences of DNAbinding domain and ligandbinding domain among these six species were from 88.6% to 97.2% and from 84.4% to 96.3% respectively, and the homologies of the amino acid sequences were from 97.6% to 100% and from 96.3% to 99.6% respectively. The results indicated that the DNAbinding domain and ligandbinding domain of PGR gene were highly conserved among mammals, and the two domains may not be the functional regions that affect the high prolificacy in sheep.

Key words: sheep; prolificacy; progesterone receptor gene; PCR-SSCP