Crossing-over between X AND Y chromosomes during ribosomal DNA magnification in Drosophila melanogaster

In genetic combinations undergoing ribosomal DNA magnification, the frequency of crossing-over between X and Y chromosomes is increased at least 20-fold above that in similar combinations not undergoing magnification. Such recombination occurs at the ribosomal DNA level. The data are consistent with a model where extra copies of ribosomal DNA are formed which, after circularization, are integrated into the chromosome.