Abstract：The 824 bp fragment of exon 2 of melatonin receptor 1A(MTNR1A ) gene was amplified successfully by PCR in both 10 ewes of nonseasonal estrous breed (Small Tail Han sheep) and 10 ewes of seasonal estrous breed (Dorset sheep), and then cloned into pGEM-T Easy vector. The positive clones were further identified by PCR and sequenced. The nucleotide sequence of exon 2 of MTNR1A gene in Small Tail Han sheep was the same as that published in GenBank (U14109). The differences in exon 2 of MTNR1A gene between Small Tail Han sheep and Dorset sheep consisted of five nucleotide changes (C329T, G355T, C566T, C580A and A675G), and homology of nucleotide sequence was 99.4%. Homologies of nucleotide sequence and amino acid sequence of exon 2 of MTNR1A gene between Small Tail Han sheep and goat, cow, pig, human, house mouse, Norway rat, Siberian hamster and chicken were 73.2% to 98.5% and 78.5% to 98.5%, respectively.
