Unequal crossing-over within theBduplication ofDrosophila melanogaster: a molecular analysis

Abstract

SummaryTheBmutation is associated with a tandem duplication of 16A1–16A7. It is unstable, mutating to wild type and to a more extreme form at a frequency of one in 1000 to 3000. The reversion to wild type is associated with the loss of one copy of the duplication, whereas the mutation to extremeBis associated with a triplication of the region. The instability ofBhas been attributed to unequal crossing-over between the two copies of the duplication. Recent molecular data show that there is a transposable element,B104, between the two copies of the duplication and support the hypothesis that this element generated the duplicationviaa recombination event. These data suggest that unequal crossing-over within the duplication may not be the cause of the instability ofB. Instead, the instability may be caused by a recombination event involving theB104element. This issue was addressed using probes for the DNA on either side of theB104element at theBbreakpoint. All of the data indicate that theB104element is not involved in the instability ofBand support the original unequal crossing-over model.