MAPPING AND MANIPULATING QUANTITATIVE TRAITS IN MAIZE

Maize has been used effectively as a model organism in the development and evaluation of molecular markers for the identification, mapping a nd manipulation of major genes affecting the expression of quantitativ e traits in plants. Although quantitative geneticists have recognized the possibility of major loci, the general dogma had emerged that quan titative traits were controlled by many loci, each with a small effect . This interpretation sent a signal to the molecular biologist not to bother with quantitative traits because it would be essentially imposs ible to isolate a gene responsible for the trait. Recent results from numerous mapping studies have shown that quantitative traits are contr olled by, at least some, factors with major effects, and have given cr edibility to the conclusion that major loci exist and that one might b e able to study them. Positive results from marker-facilitated selecti on and introgression studies have further strengthened this conclusion .