Linkage Between Chromosomal Interchanges and Colchicine Mutated Genes in Sorghum Vulgare

Although the genetic behavior of sorghum has been studied since 1916, it has never been as extensively investigated as certain other species. Information on the cytogenetics of sorghum has been slow in accumulating, chiefly because of the difficulty in distinguishing between the chromosomes. The use of chromosome structural markers as aids in cytogenetic studies has been suggested by Brink and Cooper and Burnham. Chromosomal interchanges have been used successfully in some crops to determine which chromosome pair carried specific genes or group of genes. A number of interchange lines were developed in the sorghum variety, experimental 3, by Hansel who used gamma irradiation to obtain breakage of the chromosomes. The purpose of this study was two-fold. The first objective was to test linkage relationships between the mutant genes and the break points in the interchange lines, thus determining which chromosomes carried the particular mutant genes. In addition it was desired to test for the presence of linkage between the mutant genes themselves. The second objective was to gain information on the action of colchicine in producing true-breeding mutants. If the action of colchicine were a result of somatic reduction following gene mutation, the genes affected might be expected to be scattered at random throughout the chromosome complement. Tests for linkage between the genes and the chromosome markers should provide evidence for one of these hypotheses