Polymorphism In RXFP2 In Different Sheep Breeds On The Qinghai-Tibetan Plateau Of China

Tibetan sheep, Qinghai fine wool sheep and Alpine merino are mainly sheep breeds in Qinghai-Tibet plateau of China. Tibetan sheep, a domestic breed and Qinghai fine wool sheep all exhibit typical horn types as described in Soay sheep, while Alpine merino mainly polled phenotype as Australia polled Merino. However, the molecular basis underlying the Ho locus in these sheep breeds is still elusive. Relaxin/insulin-like family peptide receptor 2 (RXFP 2) is a robust candidate gene related to horn types in sheep because of a series of independent studies association genome widely reported that underlying the existence and lack of horns. In this study, High-Resolution Melting (HRM) analysis and DNA sequencing were used to detect polymorphisms of RXFP 2 in Tibetan sheep, Qinghai fine wool sheep and Alpine merino and to determine impacts of genotype for RXFP 2 on phenotypes of horn.(1) In this study, High-Resolution Melting (HRM) analysis and DNA sequencing were used to detect polymorphisms of the RXFP 2 gene in three sheep breeds from Qinghai-Tibet plateau of China (Tibetan sheep, Qinghai fine wool sheep and Alpine merino sheep) and to determine impacts of genotype for RXFP 2 on expression of horn phenotypes. Results showed that one Single Nucleotide Polymorphisms (SNPs) was identified as RXFP 2 SNP c.29,389,966 A>G. The frequency of AA genotype of Alpine Merino Ram (poll) was significantly much higher than Tibetan sheep Ram (horn), Qinghai fine wool sheep Ram (horn) (x2(1, N=421)=72.25, P< 0.001;x2(1, N=402)=4.28, P<0.005), and the frequency of AA genotype of Qinghai fine wool sheep Ewe (poll) was also much higher than in Qinghai fine wool sheep Ewe (horn), Tibetan sheep Ewe (horn) (x2(1, N=196)=42.04, P<0.001; x2 (1, N=192)=24.69, P< 0.005).(2) The 3’-end of RXFP 2 was amplified in horned and polled animals from three sheep breeds in Qinghai-Tibet plateau of China. Sequence analysis identified a1833-bp genomic insertion located in the 3’-UTR region of RXFP 2 present in polled animals only. An efficient PCR-based genotyping method to determine the polled genotype of individual sheep is presented. Genotyping of 145 Tibetan sheep,46 Alpine Merino,139 Qinghai fine wool sheep revealed that all polled animals showed the insertion in a homozygous state and that it was absent in all horned animals. Genotyping of 46Alpine Merino sheep, an cultivated breed in which animals with poll phenotype, revealed the insertion in a homozygous state in 10 poll animals and the heterozygous state of the insertion in 36 poll animals. In conclusion, the genotyping in Alpine Merino sheep showed an association of the 1.8-kb insertion with the polled phenotype.These result indicated that these mutations could potentially be exploited in gene marker-assisted selection programs within sheep industry to select for animals with horn or poll in the future.