Deng and Lynch (1, 2) proposed to characterize deleterious genomic mutations from changes in the mean and genetic variance of fitness traits upon selfing in outcrossing populations. Such observations can be readily acquired in cyclical parthenogens. Selfing and life-table experiments were performed for two such Daphnia populations. A significant inbreeding depression and an increase of genetic variance for all traits analyzed were observed. Deng and Lynch’s (2) procedures were employed to estimate the genomic mutation rate (U), mean dominance coefficient , mean selection coefficient , and scaled genomic mutational variance ( V m /V e ). On average, ? , , and (^ indicates an estimate) are 0.84, 0.30, 0.14 and 4.6E-4 respectively. For the true values, the ? and are lower bounds, and and upper bounds.