Association between PCR-RFLP of melatonin receptor 1a gene and high prolificacy in Small Tail Han sheep

Melatonin regulates circadian rhythms and reproduction changes in seasonally reproductive mammals through binding to high-affinity, G-protein-coupled receptors. Small Tail Han sheep that has significant characteristics of high prolificacy and non-seasonal ovulatory activity is an excellent local sheep breed in P. R. China. The exon 2 of the ovine melatonin receptor 1a (MTNR1A) gene was amplified and a uniform fragment of 824 bp was obtained in 150 ewes of Small Tail Han sheep. The 824 bp PCR product was digested with restriction endonucleases Mnl I and Rsa I, and genetic polymorphism was detected by PCR-RFLP. Polymorphic Mnl I site was detected at base position 605 of the exon 2 of the MTNR1A gene. There were two kinds of genotypes in Small Tail Han sheep, AB (303 bp, 236 bp/67 bp) and BB (236 bp/67 bp, 236 bp/67 bp). The results indicated that genotype AA (303 bp, 303 bp) at Mnl I-RFLP site did not exist in non-seasonal estrous Small Tail Han sheep, which suggested that there was an association between genotype AA (303 bp, 303 bp) and reproductive seasonality in sheep. Polymorphic Rsa I site was detected at base position 604 of the exon 2 of the MTNR1A gene. Three kinds of genotypes were found in Small Tail Han sheep, AA (290 bp, 290 bp), AB (290 bp, 267 bp/23 bp) and BB (267 bp/23 bp, 267 bp/23 bp). Least squares means of litter size in the first parity and the second parity for genotype AA (290 bp, 290 bp) at Rsa I-RFLP site were 0.43 and 1.06 more than those for genotype AB (290 bp, 267 bp/23 bp) in Small Tail Han sheep.