Allelic diversity at minisatellite MS205 (D16S309): evidence for polarized variability.

We have determined the allelic structures on 106 Caucasian chromosomes at the minisatellite locus MS205 (D16S309). In addition to the internal structures deduced by minisatellite variant repeat (MVR) mapping, the genotypes at six flanking substitutional polymorphic sites have been analysed. The minisatellite structures show a polarity of variation at MS205, with most observed variation due to differences at one extremity of the tandem repeat array. This locus, therefore, provides a further example of polarity of variation at human minisatellites. Analysis of haplotypes at flanking polymorphic sites suggests that there may be a higher frequency of exchange near the highly unstable end of the minisatellite, and thus that exchanges of flanking polymorphisms may be due to co-conversion or recombination events occurring during unequal exchanges between minisatellite alleles.