Biallelic TcraV deletions in ATM-deficient thymocytes. iFISH was performed with TcraC (MBAC77) and TcraV (MBAC01, Genebank accession AF259071) BAC probes. MBAC01 contains 6 Va segments located at the extreme 5′ end of the locus. Bar graphs depict the percentage of cells (vertical axis) with 0, 2, or more than 2 TcraC (C) or TcraV (V) signals per cell. For each sample 100 to 200 nuclei were imaged and scored.