The polymorphism of the minisatellite system D2S44

• The polymorphism of the minisatellite system D2S44 comprises all the polymorphisms typical for a minisatellite sequence; from variation in fragment length caused by a restriction site polymorphism or due to variation in the number of a repeated core sequence, to a core sequence polymorphism comprising four variants and variation in the order in which these variants are iterated in tandem. All these polymorphisms can be utilised in paternity investigations, and analysis of the order of variant repeats in parent-child combinations showed that the D2S44 incompatibilities found are due to a mutation in the parental allele.The length polymorphism comprise fragments between 1.4 and 12 kbp, forming two size clusters. Different internal orders of the variant core sequences with a conserved motif at one end of the alleles can be used to group the alleles into three types. Alleles belonging to these types can be considered to be of separate ancestry and are named ancestor alleles of the red, green and yellow type. The red allele type is mainly found in one of the size clusters and the green-type in the other, while the yellow-type alleles are found in both clusters. The presence of different types of ancestor alleles might be the reason for the bimodal distribution.Analysis of 30 mutations showed that short alleles gain repeats and long ones lose repeats. The three allele types also have their ·own individual mutation patterns. Mutations in the red- and the green-type alleles are found at on end of the alleles, and in the yellow-type alleles along the whole array. In five mutations with gains of repeats the gains had most probably been generated by intra-allelic duplications. In the remaining gain mutations the origin of the repeats is not known. There is thus no clear evidence for inter-allelic exchange and mutations in the D2S44 system may mainly be caused by an exchange of sequences between sister-chromatides.VNTR polymorphism was also found in the chimpanzee but with a tandem iteration of a different non-variant core sequence, positioned upstream relative to the tandem array in man. The gorilla seems not to contain tandem repeats.The D2S44 minisatellite system, with a vast number of fragment lengths comprises astonishingly little sequence polymorphism with only a few core sequence variants and only three main allele types compared to other minisatellites. In essence it is a true VNTR marker.

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