Assignment of individuals to populations using microsatellites

The article presents two methods for the assignment of an anonymous DNA-sample to populations with known allele frequencies at a number of marker loci. The first method calculates the conditional probability for the sample to belong to one of the two possible populations given the complete marker genotype at several loci. The second method is a simple test for the sample to belong to a known population and is based on the distribution of complete marker genotype probabilities. Simulation studies were performed for the first method in order to estimate the expected probability for two populations with random allele frequency differences. The results indicate that six foci with four to five alleles each are sufficient to obtain an expected probability of more than 0.05 in 98.1 and 99.8 % of all possible situations. The simulation studies for the second method were used to estimate the power of the test for three different scenarios. The results show that with six loci with five alleles per locus a power between 0.90 and 0.98 can be achieved. However, this is only true if the distribution of allele frequencies in the known population is not extremely skewed.