MARKER-BASED INFERENCES ABOUT THE GENETIC-BASIS OF FLOWERING TIME IN MIMULUS-GUTTATUS

The genetic basis of flowering time in F-2 progeny derived from a cros s of Mimulus guttatus was studied using seven unlinked isozyme markers . Each marker represented a specific chromosomal segment; its cosegreg ation with flowering time was used to characterize genes affecting flo wering time. Three of the seven chromosomal segments were found to sho w significant, partially dominant effects on the expression of floweri ng time. These effects were relatively small, with segments marked by Me, 6Pgd2, and Tpi individually explaining only 2.3, 2.5, and 9.2 perc ent of total phenotypic variance, respectively. No significant pairwis e epistasis was observed between any marked chromosomal segments. The results of this study indicate that the quantitative variation of flow ering time in M. guttatus has a partial genetic basis, likely to consi st of multiple genes of relatively small, partially dominant effects, with the potential to respond to natural selection.