FISH results of the sampled ChrUn scaffolds mapped in UMD to chrX. Red dots close to the chrX ideogram graphically show the bioinformatics position of 21 BACs specific for the Btau unassigned scaffolds, according to the UMD (Additional Files 8 and 11). Two distinct portions of ChrUn 004.10 were mapped on UMD to two distinct, close regions of chrX (U10a and U10b in the ideogram). The green arrowhead represents the position of the reference BAC. All FISH results are in agreement with the UMD mapping, except U34 yielding only one signal (see text). BACs U9 and U44 yield signals on both chrX and chrY because they map to the pseudoautosomal region (brace) of UMD chrX (see text for details).