Changes of DNA replication behavior associated with intragenic changes of thewhite region inDrosophila melanogaster

The pattern of late labeling spots in the X chromosome ofDrosophila melanogaster has been studied by H³-thymidine autoradiography. The pattern has been found to be identical with that of the “weak spots”, or places of “ectopic pairing”. The late replicating spot in region 3C has been found to lie close to the right of the locus ofwhite. A triplication and a deficiency involving the right half of thewhite region and exhibiting changes in their interaction with the mutantzeste have been found to be associated with changes in the frequency and intensity of labeling of the late material in 3 C. Twoz ⁺ revertants derived from the triplication by X irradiation again show concomitant changes in labeling behavior at 3C.