|PAIM, TIAGO - University Of Brazil|
|Hay, El Hamidi|
|Wilson, Carrie - Welsh|
|THOMAS, MILT - Colorado State University|
|PAVIA, SAMUEL - Embrapa|
|MCMANUS, CONCEPTA - University Of Brazil|
Submitted to: Frontiers in Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2020
Publication Date: 7/10/2020
Citation: Paim, T., Hay, E.A., Wilson, C.S., Thomas, M., Kuehn, L.A., Pavia, S.R., McManus, C., Blackburn, H.D. 2020. Genomic breed composition of selection signatures in Brangus beef cattle. Frontiers in Genetics. 11. Article e00710. https://doi.org/10.3389/fgene.2020.00710.
Interpretive Summary: Crossbreeding is widely used in animal breeding. Composite breeds, as Brangus, are formed after crossbreeding to maintain uniform herds and implement breeding programs. Therefore, after formation of the composite natural and artificial selection are on going. To date it has not been clear how these selection pressures shape the genetic makeup of the composite and potentially change breed composition. Here, we identified ten genomic regions with increased homozygosity in Brangus. Five of the 10 homozygous regions in Brangus originated predominantly from Angus and the other five regions had a mixed origin, but always with Brahman contributing less than 50%. Therefore, selection and genetic drift are shaping the genetic architecture of Brangus promoting differential breed composition in specific genomic regions; this highlights the importance of selection pressures on a newly formed composite breed. And sheds light on the the selection process in composite breeds, elucidating our understanding of heterosis and complementarity at the genomic level.
Technical Abstract: Cattle breeding routinely uses crossbreeding between subspecies (B. taurus taurus and B. taurus indicus) to form composite breeds such as Brangus. This type of breedings provides an opportunity to identify recent selection signatures formed in the new population and evaluate the genomic composition of these regions of the genome. Using high dense genotyping, we first identified runs of homozygosity (ROH) and calculate genomic inbreeding. Then, we evaluated the genomic composition of the regions identified as selected (selective sweeps) using a chromosome painting approach. The genomic inbreeding increases at approximately 1% per generation after the composite breed formation, showing the need of inbreeding control even in composite breeds. Three selected regions in Brangus were also identified as Angus selection signatures. Two regions (Chromosomes 14 and 21) were identified as a selection signature in Brangus and in both the founder breeds. Five of the 10 homozygous regions in Brangus were predominantly Angus in origin (probability > 80%) and the other five regions had a mixed origin, but always with Brahman contributing less than 50%. Therefore, evolutionary events (such as drift, selection and complementarity) are likely shaping the genetic makeup of composite promoting differential breed composition in specific genomic regions, which highlights opportunities to better control the selection process in composite breeds and explore heterosis and complementarity at the genomic level.