Exceptionally High Levels of Restriction Site Polymorphism in DNA near the Maize Adh1 Gene.

Restriction maps have been prepared for the chromosomal region near seven biochemically and genetically distinct maize alcohol dehydrogenase-1 (Adh1) alleles using a small cDNA probe for Adh1. Five restriction sites spanning about 4 kb in and near the Adh1 transcription unit appear identical in all seven alleles. Outside this conserved region, variation in restriction site position is the rule. Six of the seven alleles are distinguishable, and the alleles appear to fall into four groups. The DNA flanking the 1S-type alleles seems to share no restriction site homology with the DNA near the 1F-type alleles. Several hypotheses are put forward to explain how such high levels of polymorphism could have arisen in a species that has been domesticated for only about 10,000 years.