Intercalary heterochromatin in Drosophila

The relative amount of DNA in defined segments of salivary gland chromosomes of Drosophila melangogaster from the Oregon R stock was determined by autoradiography. The data obtained were then used to estimate the possible correlation between DNA content and the degree of manifestation of charcters such as weak-point behavior, late replication, strong synapsis, breaks of chromosome rearrangements, hybridization with cRNA, and localization of mobile elements. Of 380 regions investigated 274 have showed deviations in the degree of manifestation of these features from that predicted on the basis of the DNA content of these regions. Regions, previously shown to consist of intercalary heterochromatin (IH, Zhimulev et al. 1982), were found to have a significantly higher frequency of the simultaneous manifestation of several of the above-mentioned features, with the exception of localization of mobile elements. These findings support the earlier suggestion that a high frequency and a simultaneous manifestation of IH features depend on some peculiarities of the molecular organization of IH regions, but not on a high DNA content.