Blue lines represent hypothetical variants that are drifting randomly through a population with an effective size of 100. Red lines represent hypothetical variants that are under strong selection. Drifting variants are not associated with birth date. Selected variants change in frequency over time and are strong predictors of birth date. We utilize this fact to identify selected regions of the genome.
|Bull born in 1956|
|Bull born in 2007|
Our results also suggests that the immune system is under selection in cattle. On multiple chromosomes, genes with immune functions where identified as responding to selection. Selection favors cattle that survive and reproduce by keeping pace in an "evolutionary arms race" with rapidly evolving pathogens that infect cattle. This result has been replicated in 4 additional cattle breeds, and I will be presenting this new research at the Cattle/Sheep/Goat workshop at the Plant and Animal Genome XXI Conference in January, 2013.