Comparing the diversity of the casein genes in the Asian mouflon and domestic sheep

This study makes use of data generated by the NextGen Consortium (https://www.epfl.ch/labs/nextgen/consortium).

We aimed to determine whether casein variants that are currently segregating in ovine populations existed before the domestication of sheep or, to the contrary, if their emergence is much more recent. To this end, we have retrieved whole‐genome sequences from Iranian and domestic sheep from Africa, Europe, South and East Asia and West Asia. Population structure analysis based on 55,352,935 SNPs revealed a clear separation between Iranian mouflons and domestic sheep. Moreover, we also observed a strong genetic differentiation between Iranian mouflons sampled in geographic areas close to Tehran and Tabriz. Based on sequence data, hundreds of SNPs mapping to the casein αS1 (CSN1S1, 248 SNPs), casein αS2 (CSN1S2, 268 SNPs), casein ß (CSN2, 146 SNPs) and casein κ (CSN3, 112 SNPs) genes were identified. Approximately 25–63.02% of the casein variation was shared between Iranian mouflons and domestic sheep, and the four domestic sheep populations also shared 44.2–57.4% of the casein polymorphic sites. These findings suggest that an important fraction of the casein variation present in domestic sheep was already segregating in the mouflon prior to its domestication. Genomic studies performed in horses and dogs are consistent with this view, suggesting that much of the diversity that we currently detect in domestic animals comes from standing variation already segregating in their wild ancestors.

The European Union 7th Framework Programme (FP7/2010‐2014) provided funding for the project under grant agreement no 244356‐’NextGen’. We acknowledge the support of the Spanish Ministry of Economy and Competitivity for the Centro de Excelencia Severo Ochoa 2016–2019 award (SEV‐2015‐0533). The CERCA Programme of the Generalitat de Catalunya also supported our research. Maria Luigi‐Sierra was funded with a fellowship Formación de Personal Investigador (BES‐C‐2017‐079709) awarded by the Spanish Ministry of Economy and Competitivity. Emilio Mármol‐Sánchez was funded with a PhD fellowship (FPU15/01733) granted by the Spanish Ministry of Education and Culture.

Peer reviewed