Regulatory genes -- genes that control how other genes are used -- are responsible for 69% of the heritability of dairy cattle traits such as milk production and fertility, according to a new study. This contribution is 44% more than expected and much higher than previous studies of regulatory genes in humans. The findings, reported by a team of animal and human geneticists, could improve the efficiency of agricultural breeding programs. The study also helps solve the longstanding mystery of why mammalian genomes contain so much noncoding DNA.