C(1;Y)N12 and C(1;Y)8 cytological breakpoints
Kevin Cook
Bloomington Drosophila Stock Center
Indiana University
I'd like to report the breakpoints of two aberrations. The first is T(1;Y)N12 (FBab0006842). In FBrf0036525, Jim Kennison placed the X chromosome breakpoint distal to bobbed based on rescue of the bb- lethality of C(1)DX by Ts(1Rt;YSt)N12. The Y breakpoint was placed distal to YS male fertility genes based on the fertility of males carrying Ts(1Lt;YLt)N12 and no other Y-derived chromosomal segments. From mitotic chromosome preparations stained with DAPI and chromomycin A3, I concluded that the X breakpoint lies near the h28-h29 boundary and the Y breakpoint lies distal to h24 (h28-h29;h24-YSt) based on the following cytological observations. Ts(1Lt;YLt)N12 showed DAPI-staining bands h1 through h24 on the Y and chromomycin-staining X chromosome bands h26 through h28 with no chromosome bands apparent between h24 and h28. Ts(1Rt;YSt)N12 showed the chromomycin-staining h30 band and the weakly fluorescent h29 DAPI band with no evidence for the presence of a portion of chromomycin-staining band h28.
Because all X-linked genes except bb and all Y genes are present on Ts(1Lt;YLt)N12, it can be considered a compound-XY chromosome. For simplicity, I use the synonym C(1;Y)N12.
T(1;Y)N12 was isolated as a reciprocal translocation between a normal sequence X and Dp(1;Y)BSYy+ such that C(1;Y)N12 is marked with BS (see FBrf0036525). The tip of YL in Dp(1;Y)BSYy+ carrying the BS allele consists of a portion of region 16A near the B gene and the base of the X distal to bb (see the references in FBab0003169). From Comparative Genome Hybridization microarrays of chromosomes derived from C(1;Y)N12 performed by Eric Spana at Duke University, I was able to determine that the distal breakpoint of the basal X segment lies between Release 5 coordinate  X:22228492  in fog and coordinate  X:22384175  in stnA and that genes proximal to stnA are duplicated. I could not determine the proximalmost extent of this segment, but the microarrays indicated that the duplicated segment extends at least to coordinate  X:22416503  in CG13865. I saw no evidence for a large duplicated segment encompassing the BarH1 and BarH2 genes in 16A, but the resolution of the microarrays is not high enough to exclude the possibility of a small duplicated segment from the region.
The second aberration is C(1;Y)8 (FBab0022019) from Bloomington stock 1396. C(1;Y)8 in this stock also carries Dp(3;1)P115. In mitotic preparations stained with DAPI and chromomycin A3, C(1;Y)8 looked just like Ts(1Lt;YLt)N12. It had a large chromomycin-staining h26 through h28 region juxtaposed to DAPI-stained h24 with no bands between them. Unlike T(1;Y)N12, the reciprocal Ts(1Rt;YSt) chromosome is not available for C(1;Y)8, so the mitotic breakpoints cannot be localized as precisely. Conservatively, I can say that the Y breakpoint lies distal to h24 and the X breakpoint lies somewhere distal to h29 in h26-h28 (h26-h29;h24-YSt); however, I think it's likely the breakpoint is close to the h28-h29 boundary, because the chromomycin-staining region is large and brightly fluorescent. From this banding pattern, I conclude that C(1;Y)8 lacks the X bobbed locus and that the third chromosome segment in Dp(3;1)P115 is inserted distal to bb.