Cytogenetics of nucleolus-rranspositions in Drosophila melanogaster

Summary The results from cytological identification of 125 radiation-induced specificlocus mutations revealed that the relative frequency of nucleolus-associated rearrangements could be increased substantially by selection of specific types of position-mutations for cytological analysis.One of the five nucleolus-involved rearrangements investigated was an inversion, In(1)lz^sB, and four were deletion-insertions: Tp(1)ct^6a1, Tp(1)lz⁴⁹¹, Tp(1)lz¹⁴⁴ and Dp(1;3)in^61j2.The cytomorphology of the transposed nucleolus and associated bands was easier to resolve in the salivary gland chromosomes of the rearrangements than when the nucleolus was in its normal position in the proximal region of the X-chromosome. However, the extent of the NO and adjacent chromatin involved in the transposition could not be positively delimited because of the tendency for a variegation-type alteration in the morphology of the bands adjacent to the transposed nucleolus.This investigation was supported in part by U.S. Public Health Service Research Grant, GM 15009, and in part by a grant from the Finnish National Research Council for Sciences.