6 Quantitative Genetics

Abstract

Quantitative genetics, by the broadest interpretation, is the study of any trait that can be measured on some quantitative scale. However, quantitative traits traditionally have been defined by geneticists as those traits that can only be analyzed by the application of statistical approaches. These traits have a common set of tendencies: (1) The number of genes affecting them is relatively large and usually undetermined; (2) the effects of individual genes are small; (3) the effect of environment on phenotype is large—at least as large as the overall genetic influence; and (4) as a consequence, the observed distribution of phenotypes in segregating populations is continuous. Many traits important to plant breeding are quantitative, including yield of most crop commodities and traits defining crop quality. Hence, the study of quantitative traits represents one of the most important branches of genetics.

Much of the focus of plant quantitative genetics has been on the improvement of plant breeding practices. Basic studies, aimed at increasing the understanding of the inheritance mechanisms of quantitative traits, naturally complemented the applied studies. In all cases, experimental quantitative genetic studies involve careful statistical analysis of large populations. A major effort has been invested in exploring the most efficient methods for applying artificial selection to populations toward improving quantitative traits. Much of the basic quantitative genetics research has been conducted with crop plants, such as corn, wheat, soybeans, and cotton, and often by plant breeders. Nevertheless, the need has always existed for the study of model organisms, and Arabidopsis...