DNA "fingerprinting"

    Variable Number of Tandem Repeat (VNTR) loci are chromosomal regions in which a short DNA sequence motif (such as GC or AGCT) is repeated a variable number of times end-to-end at a single location (tandem repeat). In this example, Locus A is a tandem repeat of the motif GC: there are four alleles, with two, three, four, or five repeats (A2, A3, A4, and A5, respectively). Locus B is a tandem repeat of the motif AGCT: there are only two alleles, with two or three repeats (B2 and B3, respectively).

    The example shows a southern-blot DNA fingerprint that includes both loci simultaneously. Individual #1 is heterozygous at Locus A (A2 / A5) and homozygous at Locus 2 (B2 / B2: note that this genotype gives a single-banded phenotype in the fingerprint). Individual #2 is heterozygous at both loci: (A4 / A3 and B3 / B2) respectively). The two individuals are distinguishable at either locus. Typical fingerprints include more than a dozen or VNTR loci (Homework).

Figure modified after ©1996 by Griffiths et al.; text material ©2016 by Steven M. Carr