Using QTL to Identify Genes and Pathways Underlying the Regulation and Production of Milk Components in Cattle

Milk is a complex liquid, and the concentrations of many of its components are under genetic control. Many genes and pathways are known to regulate milk compositon, and the purpose of this review is to highlight how the discoveries of quantitative trait loci (QTL) for milk phenotypes can elucidate these pathways. The main body of this review focusses primarily on QTL discovered in cattle (Bos taurus) as a model species for lactation biology, with occasional references to other ruminant species, and some comparisons with human milk composition are also presented. The following section describes a range of techniques that can be used to help identify the causative genes underlying QTL when the underlying mechanism involves the regulation of gene expression. As genotype and phenotype data bases continue to grow and diversify, new QTL will continue to be discovered, and, although proving the causality of underlying genes and variants remains difficult, these new data sets will further enhance our understanding of lactation biology.