Birth Date Selection Mapping In Four Bos taurus Breeds

We recently developed a method, Birth Date Selection Mapping, to identify loci responding to ongoing selection on quantitative phenotypes while accounting for kinship and population structure.  We fit birth date as the dependent variable in a mixed-model genome-wide association analysis.  Loci at which drift is the primary force influencing allele frequency do not experience large and directionally consistent changes in allele frequency and are not predictive of birth date.  However, loci under directional selection have relatively large, consistent changes in allele frequency over time and are predictive of birth date.  The use of a genomic relationship matrix in the mixed-model analysis explicitly accounts for relationships between samples, and deconvolutes changes in allele frequency due to selective forces and demographic changes.  We previously analyzed 3,570 Angus animals born over a 50 year period and identified selected regions putatively involved in immune function, growth, and reproductive traits.  We hypothesized that disparate breeds may be responding similarly to selection posed by  pathogens and conducted a joint analysis of 811 Herefords, 1,209 Holsteins, 2,228 Limousins, and 921 Simmental, all members of their respective North American breed registries and born over a 50 year period.  We again identified selected regions harboring genes with immune functions.  Birth Date Selection Mapping is an effective method for identifying genomic regions harboring functional mutations which are responding to selection on Mendelian or complex phenotypes.