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 anerobiosis are run in neutralpH 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 selfed 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 ofSorghum includes a gene duplication of the homologue of theAdh-1 locus inZea. Supported by USDA Grant 59-2063-01522 to NCE and KWF.