Twenty-five phenotypes were measured as indicators of bull fertility (1099 Brahman and 1719 Tropical Composite bulls). Measurements included sperm morphology, scrotal circumference, and sperm chromatin phenotypes such as DNA fragmentation and protamine deficiency. We estimated the heritability of these phenotypes and carried out genome-wide association studies (GWAS) within breed, using the bovine high-density chip, to detect quantitative trait loci (QTL). Our analyses suggested that both sperm DNA fragmentation and sperm protamine deficiency are heritable (h2 from 0.10 to 0.22). To confirm these first estimates of heritability, further studies on sperm chromatin traits, with larger datasets are necessary. Our GWAS identified 12 QTL for bull fertility traits, based on at least five polymorphisms (P < 10−8) for each QTL. Five QTL were identified in Brahman and another seven in Tropical Composite bulls. Most of the significant polymorphisms detected in both breeds and nine of the 12 QTL were on chromosome X. The QTL were breed-specific, but for some traits, a closer inspection of the GWAS results revealed suggestive single nucleotide polymorphism (SNP) associations (P < 10−7) in both breeds. For example, the QTL for inhibin level in Braham could be relevant to Tropical Composites too (many polymorphisms reached P < 10−7 in the same region). The QTL for sperm midpiece morphological abnormalities on chromosome X (QTL peak at 4.92 Mb, P < 10−17) is an example of a breed-specific QTL, supported by 143 significant SNPs (P < 10−8) in Brahman, but absent in Tropical Composites. Our GWAS results add evidence to the mammalian specialization of the X chromosome, which during evolution has accumulated genes linked to spermatogenesis. Some of the polymorphisms on chromosome X were associated to more than one genetically correlated trait (correlations ranged from 0.33 to 0.51). Correlations and shared polymorphism associations support the hypothesis that these phenotypes share the same underlying cause, i.e. defective spermatogenesis. Genetic improvement for bull fertility is possible through genomic selection, which is likely more accurate if the QTL on chromosome X are considered in the predictions. Polymorphisms associated with male fertility accumulate on this chromosome in cattle, as in humans and mice, suggesting its specialization.

中文翻译：

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X染色体变异与两个牛群中的雄性育性特征有关。

测量了二十五个表型作为公牛育性的指标（1099婆罗门和1719热带综合公牛）。测量包括精子形态，阴囊周长和精子染色质表型，例如DNA片段化和鱼精蛋白缺乏。我们估计了这些表型的遗传力，并使用牛高密度芯片在品种内进行了全基因组关联研究（GWAS），以检测数量性状基因座（QTL）。我们的分析表明，精子DNA片段化和精子鱼精蛋白缺乏都是可遗传的（h2从0.10到0.22）。为了证实这些对遗传力的初步估计，需要对具有更大数据集的精子染色质性状进行进一步研究。我们的GWAS根据每个QTL的至少5个多态性（P <10-8），确定了12个QTL用于公牛的育性性状。在婆罗门确定了五个QTL，在热带综合公牛中确定了七个。在两个品种中以及在12个QTL中有9个中检测到的大多数显着多态性大多数都在X染色体上。QTL是特定于品种的，但是对于某些性状，仔细检查GWAS结果显示可能存在单核苷酸多态性（SNP）关联（P <10−7）。例如，布拉汉（Braham）抑制水平的QTL也可能与Tropical Composites相关（同一地区的许多多态性达到P <10-7）。X染色体上精子中期形态异常的QTL（QTL峰值为4.92 Mb，P <10-17）是特定品种QTL的一个例子，在婆罗门有143个重要SNP（P <10-8）支持，但不存在在热带复合材料中。我们的GWAS结果为X染色体的哺乳动物专业化提供了证据，在进化过程中积累了与精子发生有关的基因。X染色体上的某些多态性与一个以上的遗传相关性状相关（相关性从0.33到0.51）。相关性和共享的多态性关联支持以下假设：这些表型具有相同的根本原因，即精子发生缺陷。通过基因组选择可以提高公牛的繁殖力，如果在预测中考虑X染色体上的QTL，则可能更准确。与雄性育性相关的多态性在牛的该染色体上积累，就像在人类和小鼠中一样，表明其专门化。X染色体上的某些多态性与一个以上的遗传相关性状相关（相关性从0.33到0.51）。相关性和共享的多态性关联支持以下假设：这些表型具有相同的根本原因，即精子发生缺陷。通过基因组选择可以提高公牛的繁殖力，如果在预测中考虑X染色体上的QTL，则可能更准确。牛与人和小鼠一样，与男性生殖力有关的多态性在该染色体上积累，表明其具有专门性。X染色体上的某些多态性与一个以上的遗传相关性状相关（相关性介于0.33至0.51之间）。相关性和共享的多态性关联支持以下假设：这些表型具有相同的根本原因，即精子发生缺陷。通过基因组选择可以提高公牛的繁殖力，如果在预测中考虑X染色体上的QTL，则可能更准确。牛与人和小鼠一样，与男性生殖力有关的多态性在该染色体上积累，表明其具有专门性。通过基因组选择可以提高公牛的繁殖力，如果在预测中考虑X染色体上的QTL，则可能更准确。牛与人和小鼠一样，与男性生殖力有关的多态性在该染色体上积累，表明其具有专门性。通过基因组选择可以提高公牛的繁殖力，如果在预测中考虑X染色体上的QTL，则可能更准确。牛与人和小鼠一样，与男性生殖力有关的多态性在该染色体上积累，表明其具有专门性。