ABSTRACT
In crop plants many important traits such as yield, quality and stress tolerance show continuous variation, and result from the combined action of multiple, segregating genes interacting with each other and the environment. In early investigations, before molecular markers were available, the genetics of these complex traits was studied in general terms by ‘quantitative genetics’ using statistical techniques based on means, variances and covariances of relatives, rather than in terms of individual gene effects (Mather and Jinks 1982; Falconer 1989). These analyses provided general estimates including the approximate number of loci affecting a character, the average gene action (e.g., dominance, recessiveness) and the degree to which the various polygenes interacted with each other and the environment. However, they did not provide any information about the number and location of the genes underlying quantitative traits, termed polygenes by Mather (1949).
