title: Mapping the four-horned locus and testing the polled locus in three Chinese sheep breeds.
abstract: Four-horned sheep are an ideal animal model for illuminating the genetic basis of horn development. The objective of this study was to locate the genetic region responsible for the four-horned phenotype and to verify a previously reported polled locus in three Chinese breeds. A genome-wide association study (GWAS) was performed using 34 two-horned and 32 four-horned sheep from three Chinese indigenous breeds: Altay, Mongolian and Sishui Fur sheep. The top two significant single nucleotide polymorphisms (SNPs) associated with the four-horned phenotype were both located in a region spanning positions 132.6 to 132.7 Mb on sheep chromosome 2. Similar locations for the four-horned trait were previously identified in Jacob, Navajo-Churro, Damara and Sishui Fur sheep, suggesting a common genetic component underlying the four-horned phenotype. The two identified SNPs were both downstream of the metaxin 2 (MTX2) gene and the HOXD gene cluster. For the top SNP-OAR2:g.132619300G>A-the strong associations of the AA and AG genotypes with the four-horned phenotype and the GG genotype with the two-horned phenotype indicated the dominant inheritance of the four-horned trait. No significant SNPs for the polled phenotype were identified in the GWAS analysis, and a PCR analysis for the detection of the 1.8-kb insertion associated with polled sheep in other breeds failed to verify the association with polledness in the three Chinese breeds. This study supports the hypothesis that two different loci are responsible for horn existence and number. This study contributes to the understanding of the molecular regulation of horn development and enriches the knowledge of qualitative traits in domestic animals.
authors.affiliation: Key Laboratory for Farm Animal Genetic Resources and Utilization of the Ministry of Agriculture of China, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.|CAAS-ILRI Joint Laboratory on Livestock and Forage Genetic Resources, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: He
authors.affiliation: Key Laboratory for Farm Animal Genetic Resources and Utilization of the Ministry of Agriculture of China, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.
authors.forename: Zhengkui
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Key Laboratory for Farm Animal Genetic Resources and Utilization of the Ministry of Agriculture of China, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.|CAAS-ILRI Joint Laboratory on Livestock and Forage Genetic Resources, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.
authors.forename: Yabin
authors.initials: Y
authors.lastname: Pu
authors.affiliation: Key Laboratory for Farm Animal Genetic Resources and Utilization of the Ministry of Agriculture of China, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.|CAAS-ILRI Joint Laboratory on Livestock and Forage Genetic Resources, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Chen
authors.affiliation: Key Laboratory for Farm Animal Genetic Resources and Utilization of the Ministry of Agriculture of China, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China. yuehui.ma@263.net.|CAAS-ILRI Joint Laboratory on Livestock and Forage Genetic Resources, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China. yuehui.ma@263.net.
authors.forename: Yuehui
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Key Laboratory for Farm Animal Genetic Resources and Utilization of the Ministry of Agriculture of China, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China. jianglin@caas.cn.|CAAS-ILRI Joint Laboratory on Livestock and Forage Genetic Resources, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, 100193, China. jianglin@caas.cn.
authors.forename: Lin
authors.initials: L
authors.lastname: Jiang
mesh_terms: D000818:Animals; D001947:Breeding; D002681:China; D002874:Chromosome Mapping; D005787:Gene Frequency; D056726:Genetic Association Studies; D005838:Genotype; D006733:Horns / Q000254:growth & development*; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D034561:Sheep, Domestic / Q000235:genetics*
keywords: Ovis aries; four-horned phenotype; genome-wide association study