Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.
Department of Science, Waterford Institute of Technology, Cork Road, Co. Waterford, Ireland.
J Anim Sci. 2021 May 1;99(5). doi: 10.1093/jas/skab070.
Sexual dimorphism, the phenomenon whereby males and females of the same species are distinctive in some aspect of appearance or size, has previously been documented in cattle for traits such as growth rate and carcass merit using a quantitative genetics approach. No previous study in cattle has attempted to document sexual dimorphism at a genome level; therefore, the objective of the present study was to determine whether genomic regions associated with size and muscularity in cattle exhibited signs of sexual dimorphism. Analyses were undertaken on 10 linear-type traits that describe the muscular and skeletal characteristics of both males and females of five beef cattle breeds: 1,444 Angus (AA), 6,433 Charolais (CH), 1,129 Hereford, 8,745 Limousin (LM), and 1,698 Simmental. Genome-wide association analyses were undertaken using imputed whole-genome sequence data for each sex separately by breed. For each single-nucleotide polymorphism (SNP) that was segregating in both sexes, the difference between the allele substitution effect sizes for each sex, in each breed separately, was calculated. Suggestively (P ≤ 1 × 10-5) sexually dimorphic SNPs that were segregating in both males and females were detected for all traits in all breeds, although the location of these SNPs differed by both trait and breed. Significantly (P ≤ 1 × 10-8) dimorphic SNPs were detected in just three traits in the AA, seven traits in the CH, and three traits in the LM. The vast majority of all segregating autosomal SNPs (86% in AA to 94% in LM) had the same minor allele in both males and females. Differences (P ≤ 0.05) in allele frequencies between the sexes were observed for between 36% (LM) and 66% (AA) of the total autosomal SNPs that were segregating in both sexes. Dimorphic SNPs were located within a number of genes related to muscularity and/or size including the NAB1, COL5A2, and IWS1 genes on BTA2 that are located close to, and thought to be co-inherited with, the MSTN gene. Overall, sexual dimorphism exists in cattle at the genome level, but it is not consistent by either trait or breed.
性二型，即同一物种的雄性和雌性在某些外观或体型特征上存在明显差异的现象，此前已在牛中使用定量遗传学方法对生长速度和胴体质量等性状进行了记录。在牛中，以前没有试图在基因组水平上记录性二型现象；因此，本研究的目的是确定与牛的大小和肌肉发达程度相关的基因组区域是否存在性二型的迹象。对五个牛肉品种的雄性和雌性共 10 个线性特征进行了分析：1444 头安格斯牛（AA）、6433 头夏洛莱牛（CH）、1129 头赫里福德牛、8745 头利木赞牛（LM）和 1698 头西门塔尔牛。按品种分别对每只性别的全基因组序列数据进行了全基因组关联分析。对于在两性中分离的每个单核苷酸多态性（SNP），分别计算了每个品种中两性等位基因替代效应大小的差异。在所有品种的所有性状中，都检测到了两性中分离的、提示性（P ≤ 1×10-5）的性二态 SNP，尽管这些 SNP 的位置因性状和品种而异。仅在 AA 中检测到三个性状、CH 中检测到七个性状和 LM 中检测到三个性状存在显著性（P ≤ 1×10-8）的二态 SNP。绝大多数分离的常染色体 SNP（AA 中的 86%到 LM 中的 94%）在两性中具有相同的次要等位基因。在两性中分离的所有常染色体 SNP 中，有 36%（LM）到 66%（AA）的 SNP 观察到了性别间等位基因频率的差异（P ≤ 0.05）。二态 SNP 位于与肌肉发达程度和/或体型相关的多个基因内，包括位于 BTA2 上的 NAB1、COL5A2 和 IWS1 基因，这些基因靠近 MSTN 基因，并被认为与其共同遗传。总体而言，牛在基因组水平上存在性二型现象，但无论是性状还是品种，这种现象都不一致。
