The tri-allelic pattern was inherited from grandmother to granddaughter through the paternal line. The researchers believe that this pattern at this locus has not been reported previously in the literature, although six tri-allelic patterns were reported on the short tandem repeat DNA Internet Database. The inheritance of the allele through two generations was evidence that the allele was caused by duplication rather than by a somatic mutation at a heterozygous region. Aberrant DNA profiles can result from a number of biological processes, including somatic mutations, mosaicism, deletions, and duplications. Short tandem repeat (STR) genotyping of other markers did not show duplication of any part of chromosome 3, although the resolution of markers on chromosome 3p21 was not very high. This does not exclude possible small duplications between marker D3S1358 and the closest markers tested, D3S1768 and D3S1358g. This region on chromosome 3p21 was reported to show instability, including deletions and duplication in a number of solid tumors. This suggests that duplications at this region might also be of medical importance. 1 table, 2 figures, and 13 references