Showing results for: [ Animal Developmental and Reproductive Biology ]
X chromosome variants were associated to heritable fertility traits, in two bovine populations.
Fortes, Porto-Neto et al. 2020.
Background: Targeting phenotypes related to bull fertility, such as spe... morerm morphology and sperm DNA fragmentation can help identify mutations that limit reproduction capacity. Twenty-five fertility-related phenotypes were measured as indicators of bull fertility (1,099 Brahman bulls and 1,719 Tropical Composite bulls). Measurements included standard bull breeding soundness evaluation (e.g. sperm motility and morphology), scrotal circumference, and sperm DNA fragmentation and sperm protamine deficiency. These phenotypes were used in genome-wide association studies (GWAS) that aimed to estimate heritability and detect quantitative trait loci (QTL).
Results: Genomic analyses suggest that bull fertility traits have a heritable component, which makes selective breeding possible. The phenotype variation in sperm DNA fragmentation and sperm protamine deficiency traits have a heritable component (h2 ~ 0.05 – 0.22). These first estimates for heritability of sperm chromatin phenotypes require further studies, with larger datasets, to corroborate present results. Our GWAS identified eleven QTLs for bull fertility traits, based on five or more significant SNPs (P < 10-8). Six QTLs were identified in Brahman and five in Tropical Composite bulls. Most of the significant polymorphisms in both breeds and eight out of the eleven QTLs mapped to chromosome X. The autosomal QTLs were for sperm DNA fragmentation mapping to chromosome 11 (Brahman), for Inhibin mapping to chromosome 2 (Brahman), and for scrotal circumference mapping to chromosome 5 (Tropical Composites). The QTLs were breed specific, but for some traits, a closer inspection of GWAS reveals suggestive SNP associations (P < 10-7) in both breeds. For example, the Inhibin QTL observed in Braham might be relevant to Tropical Composites too, because we observed an association peak in that same region (many SNPs reaching P < 10-7). An example of breed specific results was the QTL for sperm midpiece morphological abnormalities, in the X chromosome (QTL peak at 4.92 Mb, P < 10-17). This QTL was supported by 487 significant polymorphisms (P < 10-8) in Brahman and yet it was absent in Tropical Composites. The reported GWAS add evidence to a mammalian specialization of X that evolved to harbor genes linked to spermatogenesis, as similarly observed in mice and humans. Some variants in X may affect more than one genetically correlated trait (r2 ~ 0.33 – 0.51), such as sperm morphology and sperm DNA fragmentation. Correlations and shared SNP associations support the hypothesis that these phenotypes have the same underlying cause: faulty spermatogenesis.
Conclusions: Genetic improvement for bull fertility is possible through selective breeding. Genomic selection for bull fertility might be more accurate if the X chromosome mutations that underlie the discovered QTL are included in the analyses. Polymorphisms associated with bull fertility accumulate in the X chromosome, as they do in humans and mice, thus, suggesting specialization of this chromosome.less
MLA: L.GEN.1818 Bull fertility update: historical data, new cohort and advanced genomics - Livestock genetics and genomics - Published 10 Mar 2020
Collection contains semen from bulls from the Boran-Tuli Importation Program in 1991 and part of the Belmont Beef Breeding Program from the late 1970s through to 2011. The collection comprises several... more thousand straws associated with the development of tropically adapted Bos taurus and Bos indicus cattle. less
Legacy data - Biological Specimen Collections - Published 12 Nov 2012