A quantitative trait is a given phenotypic trait influenced by the combined effects of many genes and its environment. A quantitative trait locus (QTL) is a region of DNA (i.e., a <em>locus</em>) associated with the variation of a quantitative trait. In the last years, some QTLs correlated to the variation of HDL, LDL, and triglycerides levels were mapped in different genomic regions, thereby showing that these complex traits are regulated by the interaction of multiple genetic <em>loci</em>.
