Selection and Complex Multigene Traits

Abstract

Abstract Phenotypic characters that display continuous variation are usually called ‘quantitative traits’ or ‘complex traits’. Alternatively, geneticists refer to them as ‘multigene traits’, because the underlying genetic architecture is assumed to be polygenic. Analyses of the genetic architecture of diverse quantitative traits suggest that the number of loci (quantitative trait loci, QTLs) affecting trait variation can be very different. Moreover, experimental studies report contrasting genetic architectures, where either large‐effect QTLs or small‐effect QTLs explain most of the phenotypic variation. In addition, recent reports highlight the pervasiveness of epistasis. Considerable evidence, obtained with the QST–FST methodology, supports the idea that natural selection plays a key role in the evolution of complex traits. Nevertheless, the identification of a representative number of genes underlying QTLs is necessary to determine the contribution of selection, drift and gene flow for the evolution of complex traits. Key Concepts: The phenotypic variation in complex traits is usually determined by multiple genes. Understanding the genetic architecture of complex traits begins with the identification and characterisation of quantitative trait loci (QTLs). The search for the genes that harbour naturally segregating variation affecting quantitative traits is commonly performed through linkage QTL mapping. An analysis of the genetic architecture of different characters suggests that the number of QTLs contributing to a trait can be very different. Researchers aim to discover the genes (QTGs) and nucleotides (QTNs) underlying QTL effects. The comparison of the statistics of QST and FST is one of the most popular methods employed to search for the signature of natural selection on quantitative traits. Considerable evidence supports the idea that natural selection is a key player in the evolution of complex traits. The identification of a representative number of QTGs is necessary to determine the contributions of selection, drift and gene flow for the evolution of complex traits.