MARKER-BASED INFERENCES ABOUT FECUNDITY GENES CONTRIBUTING TO INBREEDING DEPRESSION IN MIMULUS-GUTTATUS

Eight unlinked isozyme loci were used as genetic markers to characteri ze fecundity genes contributing to inbreeding depression in two selfed progeny arrays of Mimulus guttatus. Five fecundity traits were measur ed. Six of eight marked chromosomal segments were significantly associ ated with the expression of these traits. The number of detected for f ive traits in two progeny arrays varied, with an average of 2.8 genes per trait. Individual segments explained 1.44-9.29%, and together acco unted for 3.85-11.32%, of phenotypic variation. Of 20 significant asso ciations, 10 could be interpreted as exhibiting partial dominance, 7 o verdominance, 3 partial recessivity, and 0 under-dominance. Significan t pairwise epistasis was rare. The results of this study suggest that inbreeding depression is caused by many deleterious genes of relativel y small, partially dominant effects.