Alcohol dehydrogenase isozymes in grain sorghum (Sorghum bicolor): evidence for a gene duplication

Two sets of alcohol dehydrogenase (ADH) bands are regularly observed in grain sorghum (Sorghum bicolor): set I is a permanent triplet; set II is variable, as either two or three bands. A faint set III is detected only when extracts from seeds subjected to anaerobiosis are run in neutral pH gels. Dissociation-reassociation experiments reveal that the central band of the set I triplet is a heterodimer of the other two. Full-sib progeny analysis from self-fed plants shows that the set II bands are doublets, with heterozygotes having only three apparent bands instead of four because of the similar mobilities of the fast-migrating isozyme specified by the slow allele and the slow isozyme specified by the fast allele. We propose a three-locus model as the best explanation of these patterns. Set I consists of the products of two loci and their intergenic heterodimer. Set III is specified by a third locus. Set II isozymes are the intergenic heterodimers of the two set I loci and the set III locus. This explanation is similar to that of Schwartz and Freeling for maize but suggests that the evolution of Sorghum includes a gene duplication of the homologue of the Adh-1 locus in Zea.