DNA dinucleotide evolution in humans: Fitting theory to facts

We examine length distributions of similar to 6000 human dinucleotide micro satellite loci, representing chromosomes 1-22, from the GDB database. Under the stepwise mutation model, results from theory and simulation are compar ed with the empirical data. In both constant and expanding population scena rios, a simple single-step model with parameters chosen to account for the observed variance of microsatellite lengths produces results inconsistent w ith the observed heterozygosity and the dispersion of length skewness. Comp licating the model by allowing a variable mutation rate accounts for the ho mozygosity, and introducing a small probability of a large mutation step ac counts for the dispersion in skewnesses. We discuss these results in light of the long-term evolution of microsatellites.