Complex mutational events at the HumD21S11 locus.

We have studied length and sequence variability at the HumD21S11 locus in five different populations to obtain more detailed information about the structure of this short tandem repeat system. In all populations studied so far two types of alleles have been described. The consensus alleles (type I) consist of three regions with variable numbers of TCTR units and one constant region comprising 43 bp. Alleles of type II (so-called interalleles) show the same basic sequence structure except for the occurrence of a TA insertion at a fixed position in variable region 3. Additional sequence variability exists in the Ovambo and Papuan populations with gross changes in two of the three variable regions and in the constant region. Due to these extreme variations the Ovambos and Papuans showed a better fit to the infinite allele model than to the stepwise mutation model. In the German, Japanese and Chinese populations no significant bias towards one of the two models could be observed. Population genetic studies showed no significant deviation from Hardy-Weinberg equilibrium.