The tip of YL in C(1;Y)N12 contains a portion of region 16A near the B gene and the base of the X distal to bb (this is because T(1;Y)N12 was isolated from a reciprocal translocation between a normal sequence X and Dp(1;Y)BSYy+). Comparative Genome Hybridization microarrays of chromosomes derived from C(1;Y)N12 indicate that the distal breakpoint of this basal X segment lies between Release 5 coordinate X:22228492 in fog and coordinate X:22384175 in stnA. In addition, genes proximal to stnA are duplicated in this segment. The proximalmost extent of this segment extends at least to coordinate X:22416503 in CG13865. No evidence has been see for a large duplicated segment encompassing the B-H1 and B-H2 genes in 16A using Comparative Genome Hybridization microarrays, but the resolution of the microarrays is not high enough to exclude the possibility of a small duplicated segment from the region.