ISOLATION AND ANALYSIS OF THE BREAKPOINT SEQUENCES OF CHROMOSOME INVERSION IN(3L)PAYNE IN DROSOPHILA-MELANOGASTER

Chromosomal rearrangements constitute a significant feature of genome evolution, and inversion polymorphisms in Drosophila have been studied intensely for decades. Population geneticists have long recognized that the sequence features associated with inversion breakpoints would reveal much about the mutational origin, uniqueness, and genealogical history of individual inversion polymorphisms, but the cloning of breakpoint sequences is not trivial. With the aid of a method for rapid recovery of DNA clones spanning rearrangement breakpoints, we recover and examine the DNA sequences spanning the breakpoints of the cosmopolitan inversion In(3L)Payne in Drosophila melanogaster. By examining the sequence diversity associated with six standard and seven inverted chromosomes from natural populations, we find that the inversion is monophyletic in origin, the sequences are genetically isolated from recombination at the breakpoints, and there is no association with features such as transposable elements. The inverted sequences show 17-fold less nucleotide polymorphism, but there are eight fixed differences in the region spanning both breakpoints. This suggests that this inversion is not recently derived. Finally, Northern analysis and transcript mapping find that the distal breakpoint has disrupted three transcripts that are normally expressed in the standard arrangement. Incidentally, the method introduced here can be used to isolate breakpoint sequences of arrangements associated with many human diseases.