The first simulation technique used in pedigree analysis was not MCMC but rather the Monte Carlo simulation of independent observations. Mac Cluer et al. [9] developed gene dropping. In this method, founder genotypes are first simulated according to population frequencies. The genes are ``dropped'' down the pedigree by simulating gene flow according to Mendel's laws. Finally, the phenotypes are simulated from the genotypes according to the penetrances. Simulated phenotypes are then compared to the observed phenotypes, and outcomes inconsistent with the observed phenotypes are discarded. The result is a random sample of genotypes given the observed phenotypes. The method works well only on small pedigrees. With larger genealogies, the proportion of outcomes compatible with the data becomes very small and most of the generated observations are discarded.