Dr. Bennett's research determines the associations of genetic markers (SNPs) with economically important traits in cattle. An SNP is a single nucleotide difference (polymorphism) in the genome sequence. SNPs can cause genetic differences in performance or can be closely linked to causal genetic differences. A difficulty in estimating SNP associations is that some SNPs are found at low frequencies in cattle populations. A low frequency SNP leads to few homozygous (two copies of the SNP) animals. In turn, this reduces (1) the reliability of estimated associations, (2) the ability to determine dominance or recessiveness of SNP associations, and (3) the ability to estimate interactions of SNP associations. An experiment to more accurately estimate associations for some SNPs is being conducted. Four populations of cattle are being selected for intermediate frequencies of different combinations of two or three SNPs. Associations of SNPs with survival, growth, meat, and reproductive traits will be estimated. Knowing the full spectrum of trait associations with an SNP will be useful for cattle selection.