The intergenic spacer (IGS) region of the bb fragment contains 11-12 240bp repeats, in contrast to the 6 copies present in the progenitor (bbr10Δ3). There is also a tandem duplication of a 450bp segment of rDNA flanking the promoter.
Increases the frequency of nondisjunction X-Y seen in Df(1)X-1/Dp(1;Y)BSYy+ males.