Connecting QTLS to the g-matrix of evolutionary quantitative genetics

Abstract

Evolutionary quantitative genetics has recently advanced in two distinct streams. Many biologists address evolutionary questions by estimating phenotypic selection and genetic (co)variances (G matrices). Simultaneously, an increasing number of studies have applied quantitative trait locus (QTL) mapping methods to dissect variation. Both conceptual and practical difficulties have isolated these two foci of quantitative genetics. A conceptual integration follows from the recognition that QTL allele frequencies are the essential variables relating the G-matrix to marker-based mapping experiments. Breeding designs initiated from randomly selected parental genotypes can be used to estimate QTL-specific genetic (co)variances. These statistics appropriately distill allelic variation and provide an explicit population context for QTL mapping estimates. Within this framework, one can parse the G-matrix into a set of mutually exclusive genomic components and ask whether these parts are similar or dissimilar in their respective features, for example the magnitude of phenotypic effects and the extent and nature of pleiotropy. As these features are critical determinants of sustained response to selection, the integration of QTL mapping methods into G-matrix estimation can provide a concrete, genetically based experimental program to investigate the evolutionary potential of natural populations.

Figure 1

The number of citations per year to Lande and Arnold (1983, diamonds) and Lander and Botstein (1989, squares) was estimated using Web of Science (Thomson Reuters, Philadelphia, PA). The number of publications citing both papers (triangles) was determined by comparing these lists.

Figure 2

The Replicated F2 mapping design: A collection of n randomly extracted inbred lines is each crossed to a common reference line (RL). Each cross produces F1s that are subsequently intracrossed (or self-fertilized) to produce an F2 family. Arrows represent transmission of a gamete.

Figure 3

The distribution of estimates is given for two distinct sets of simulations of the Replicated F2 design. Each distribution is composed of 200 replicate experiments. Red bars denote results where the true frequency of the reference line (RL) allele is 0.05 whereas green bars are for cases in which q = 0.5.