NOVEL MUTATION PROCESSES IN THE EVOLUTION OF A HAPLOID MINISATELLITE,MSY1 - ARRAY HOMOGENIZATION WITHOUT HOMOGENIZATION

The Y-specific locus MSY1 is the only known haploid minisatellite, and displays an extremely high degree of structural diversity which can b e assayed by minisatellite variant repeat PCR (MVR-PCR). One group of alleles, in an African-specific class of Y chromosomes (haplogroup 8), behaves unusually in the conventional MVR-PCR assay, and sequencing d emonstrates that this is because repeat units in these alleles contain an additional base substitution, We have designed a new MVR-PCR syste m to detect these novel variants, and show firstly that they are confi ned to the haplogroup 8 chromosomes, and secondly that the base substi tution has spread through these arrays without the elimination of exis ting repeat variants, The sharing of a particular base substitution be tween otherwise distinct repeat types in these alleles represents evid ence of a remarkable mutation process in their evolutionary history, i n which the variant base must have been spread by a biased repair mech anism operating in very small patches within heteroduplexes.