The One Band-One Gene Hypothesis: Evidence from a Cytogenetic Analysis of Mutant and Nonmutant Rearrangement Breakpoints in Drosophila Melanogaster

Fundamental questions relating to the organiza-tion of eukaryotic chromosomes have been profitably attacked by recent cytogenetic nvesti-gations on polytene chromosomes of Drosophila melanogaster For example, Judd et al. (1972) have demonstrated that in the zeste-white (z-w) interval, only one genetic function is associated with each visible band or chromomere. Other studies have shown that the centric "hetero-chromatin " (in which repetitive DNA is concen-trated) is not polytenized (Rudkin, 1969; Gall et al., 1971). Further, the amount of crossing-over between two cytologically localized genes has been correlated with the quality of the bands, i.e., their DNA content, not simply with the number of bands