Abstract: According to the human, chicken and rat sequence of exon 4 of estrogen receptor (ESR) gene, a pair of primer was designed. DNA fragment of exon 4 of Small Tail Han sheep ESR gene was amplified successfully by PCR, and was cloned into pGEM-T Easy vector. The positive clones were further identified by PCR. The nucleotide sequence was detected and the amino acid sequence of this fragment was deduced. The comparison of the fragment of exon 4 of Small Tail Han sheep ESR gene with that of human, cattle, pig, rat and chicken ESR gene showed that the homologies of the nucleotide sequence and amino acid sequence of the fragment with human, cattle, pig, rat and chicken were from 77.68% to 97.28% and from 71.82% to 98.18%, respectively, which indicated that the ESR gene was highly conserved. Nucleotide sequence existed one special variation and the peptide sequence of amino acids 23 to 36 was highly variable in Small Tail Han sheep.

Key words: Small Tail Han sheep; estrogen receptor gene; cloning; sequence analysis