FOUNDER EFFECT - ASSESSMENT OF VARIATION IN GENETIC CONTRIBUTIONS AMONG FOUNDERS

We present a Monte Carlo method for determining the distribution of fo unders' genetic contributions tb descendant cohorts. The simulation of genes through known pedigrees generates the probability distributions of contributed genes in recent cohorts of descendants, their means, a nd their variances. Genealogical data from three populations are analy zed: the Hutterite population of North America, the island population of Sottunga from the Aland archipelago, and the large Utah Mormon popu lation. Two applications of the Monte Carlo method are presented. Firs t we investigate the relative opportunity for founder effect in the th ree populations, which have dissimilar pedigree structures and dissimi lar disease gene frequencies. Second, we measure the reproductive succ ess of population founders in terms of the number of genes they contri bute to a cohort some number of generations descendant and compare the effects of polygyny versus monogamy on reproductive success. The dist ribution of Hutterite founder contributions describes the context for a classic founder effect. Hutterite founders have a higher probability of leaving no genes in the population (72%) than Sottunga (48%) and M ormon (48%) founders. However, founder genes that survive among Hutter ite descendants do so in larger numbers on average than founder genes in the other two populations. Greater variation among monogamous Hutte rite founders compared with Mormon polygynous founders demonstrates th at polygyny alone does not maximize the variance in reproductive succe ss; other population characteristics are at least as important for det ermining variability among individuals in their genetic contributions to a gene pool. Our findings make it difficult to appreciate the repro ductive advantage of polygyny in the Mormon population. Although the e xpected gene contributions and their variances were larger for polygyn ous founders compared with other Mormons, the main effect of polygyny was to increase the probability that any polygynist left a few genes a mong descendants. Furthermore, only 12% of the variation in the geneti c contributions of Mormon founders is explained by their number of off spring. We conclude that shallow genealogical data (from one or a few generations) provide a poor measure of long-term reproductive success.