FIG. 2.

Metaphase chromosomes from the GM10115-derived clone GH24. (Top left) FISH with a biotinylated probe to the pCMV-EGFP2Xho HR substrate. A single hybridization signal is arrowed. (Top right, bottom left, and bottom right) FISH with fluorescence-labeled probes to the T₂AG₃(n) interstitial telomeric-like repeat (digoxigenin labeled, red) and human chromosome 4 (biotinylated labeled, green). (Top right) Control unirradiated metaphase cell. (Bottom left and right). Two metaphase cells from a clonally expanded cell surviving 1 Gy of X-irradiation, illustrating instability of the human chromosome and how it can recombine with the hamster chromosomes at the interstitial telomeric sites.