Genetic analysis of the hypervariable region flanking the human insulin gene

In order to study the mechanisms for the generation of length diversity within the 5' flanking region of the human insulin gene, we have isolated and sequenced a previously uncharacterized allele. This allele, of a size intermediate between those three already described in the literature, encompasses 1,156 base pairs (bp) and contains 81 reiterated tandem oligonucleotides of 14-15 bp each. Population analysis on 298 independently sampled individuals by Southern blotting of genomic DNA demonstrates that the polymorphic portion of the insulin 5' flanking region varies from 400 to more than 8,000 nucleotides, being encoded by from 30 to over 540 oligomeric repeats. Length variability 5' to the insulin gene is a result primarily of unequal crossing over, which generates an expansion or contraction in the number of tandem repeat units per chromosome. A similar mechanism probably accounts for nondispersed reiterated sequences at other loci in the human genome.