Quantitative traits are those that vary continuously. This is in contrast to qualitative traits, in which the phenotype is discrete and can take on one of only a few different values. Examples of quantitative traits include height, weight, and blood pressure. There is no single gene for any of these traits, instead it is generally believed that continuous variation in a trait such as blood pressure is partly due to DNA sequence variations at multiple genes, or loci. Such loci are referred to as quantitative trait loci (QTL). Much of how we study and characterize quantitative traits can be attributed to the work of Ronald Fisher and Sewall Wright, accomplished during the first half of the twentieth century.

The Genetic Architecture of Quantitative Traits

An important goal of genetic studies is to characterize the genetic architecture of quantitative traits. Genetic architecture can been defined in one...