Retains six IGS repeats plus about 2kb from the 5' end of the rDNA transcription unit.
Construct: bb fragment extends from the 3' end of 28S through the middle of the 18S gene, includes the intergenic spacer (IGS) and external transcribed sequences (ETS).
Heterozygotes with Dp(1;Y)BSYy+ display significant stimulation of X-Y disjunction in adult testes when recombined with Df(1)X-1, in genetic and cytological assays. Effect is increased with two copies of bbr10. No mininucleolus is formed.