High gene flows promote close genetic relationship among finewool sheep populations （Ovis aries） in China

The aim of our present study was to construct genetic structure and relationships among Chinese fine-wool sheep breeds. 46 individuals from 25 breeds or strains were genotyped based on the Illumina Ovine 50K SNP array. Meanwhile, genetic variations among 482 individuals from 9 populations were genotyped with 10 microsatellites. In this study, we found high genetic polymorphisms for the microsatellites, while 7 loci in the Chinese superfine Merino strain （Xinjiang types） （CMS） and 5 loci in Gansu alpine superfine-wool sheep strain （GSS） groups were found deviated from Hardy-Weinberg equilibrium （HWE）. Genetic drift FsT=0.019 （P〈0.001） and high gene flows were detected in all the 7 fine-wool sheep populations. Phylogenetic analysis showed fine-wool sheep populations were clustered in a group independent from the Chinese indigenous breeds such that the 7 fine-wool sheep clustered distinct from Liangshan semifine-wool sheep （LS） and Hu sheep （HY） reflected by different population differentiation analyses. Overall, our findings suggested that all fine-wool sheep populations have close genetic relationship, which is consistent with their breeding progress. These populations, therefore, can be regarded as open-breeding populations with high levels of gene flows. Furthermore, the two superfine-wool strains, viz., CMS and GSS, might be formed by strong artificial selection and with frequent introduction of Australian Merino. Our results can assist in breeding of superfine-wool sheep and provide guidance for the cultivation of new fine-wool sheep breeds with different breeding objectives.