SINGLE-BASE SUBSTITUTIONS GIVE RISE TO A 5-BANDED DNA PROFILE AT THE D10S28 LOCUS

Background: DNA profiles from variable number of tandem repeat (VNTR) loci typically are composed of two bands, one derived from each member of the homologous pair of chromosomes. DNA profiles composed of more than two bands result from mutations, and the question arises as to th e mechanism underlying these unusual multibanded DNA profiles. Study D esign and Methods: An alleged father in a paternity test was found to have a five-banded DNA profile at the D10S28 locus when his DNA was su bjected to single-locus restriction fragment length polymorphism mappi ng with the restriction enzyme Pvu II. Results: Several results sugges t that this complex DNA profile is the result of several single-base c hanges within the VNTR locus. First, there was no evidence of partial digestion of the DNA with Pvu II. Furthermore, the multibanded allele happened, in this case, to be transmitted to the child, who also showe d a five-banded pattern composed of four bands inherited from the alle ged father and one band inherited from the mother. Second, digestion o f this DNA with Hae III resulted in the visualization of just two band s at the D10S28 locus. Conclusion: The results confirm the notion that mutations at VNTR loci are not always the result of additions or dele tions of tandem repeats, but that they can also involve single-base su bstitutions either within or flanking VNTR loci that give rise to atyp ical DNA profiles and new alleles at the locus.