Title: Dinucleotide repeat polymorphism at the D21S168 locus
Abstract: A 0.6 kb TaqI fragment was isolated from plasmid pVNTR-B; pVNTR-B represents a subcloned fragment from the ABR gene (1).Polymorphism: TaqI cuts within VNTR-B of the ABR gene generating 1-4 different sized alleles per individual when hybridized with the 0.6 kb probe (see figure).HinfI also cuts within the VNTR.The enzymes BamHI, BglII, BstEII, EcoRI, HindIfi and SstI cut outside of the VNTR generating one fragment per allele (1).However, the large sizes of the alleles make it difficult to differentiate between different-sized alleles.Frequency: Conventional frequency calculations are not possible when the number of different sized fragments seen per individual is variable.Frequencies are given as the fraction of individuals in whom the band was present without regard to intensity (2).Calculations are based on DNAs from 49 unrelated individuals digested with TaqI.2.05 kb = 0.041, 1.75 = 0.16, 1.51 = 0.10, 1.35 = 0.061, 1.25 = 0.28, 1.05 = 0.12, 0.7 = 0.33, 0.67 = 0.14, 0.54 = 0.02, 0.47 = 0.84, 0.37 = 0.082 and 0.28 = 0.041.Heterozygosity: A heterozygosity of 78% was observed in 49 unrelated individuals.Cannot be determined; see frequency.Chromosomal Localization: Initially ABR was localized to 17pl3 (1).More detailed in situ hybridization to normal and chromosome 17 derivative metaphase spreads support a localization to 17pl3.3 (C.Morris, unpublished results).Mendelian Inheritance: Co-dominant segregation was observed in 3 pedigrees.