Multicolor FISH with a telomere repeat and Sry sequences shows that Sxr (Sex reversal) in the mouse is a new type of chromosome rearrangement.

XYSxr (Sex reversal) mice carry a Y chromosome in which the chromatin (including Sry, the gene for testis determination) that normally resides on the short arm is duplicated and the second copy is relocated to the distal end of the long arm. Multicolor in situ hybridization to mitotic chromosomes of XYSxr males using probes for the telomere repeat sequence (TTAGGG)n and Sry shows that the rearranged chromatin is located distal to the telomeric signal. This suggests that the rearrangement arose from a recombination event involving the distal Y telomere sequences, i.e., within the telomere, a structure historically assumed to be incapable of participating in chromosome rearrangements.