Inferring the recent ancestry of myostatin alleles affecting muscle mass in cattle.

Double muscling is an inherited condition in cattle characterised by large increases in muscle mass. Mutations in the myostatin (MSTN) gene, responsible for double muscling, were targeted in this study to estimate the time since the most recent common ancestor (TMRCA) for Q204X (p.Gln204*), E226X (p.Glu226*), 821del11 (c.821del11), E291X (p.Glu291*), C313Y (p.Cys313Tyr) and the more phenotypically moderate F94L (p.Phe94Leu) mutation. Genetic variability was examined in eight regions upstream and downstream of the MSTN locus. The molecular distance of the homozygous region associated with each MSTN allele was used to estimate the TMRCA. Long homozygous segments were associated with the MSTN alleles (mostly > 2 Mb), compared to short segments (130 kb) for cattle wild type at the double muscling and F94L sites. Estimates of time indicated that each MSTN allele had a recent common ancestor (<400 years ago). The results from this study, and the increasing frequency of these MSTN alleles in some cattle breeds, demonstrate recent positive selection.