FANCD2i and FANCAi hESCs exhibit increased chromosomal breakage and radial formation upon MMC treatment. (A-B) Representative metaphase spreads from FANCAi and FANCD2i hESCs after treatment with 200nM MMC for 24 hours. DEL indicates deletion; CTB, chromatid break; CTG, chromatid gap; and CSB, chromosome break. (C) Quantification of total damage/cell (additional details on breakage score calculation in “Chromosomal breakage analysis”) and quadriradials/complex damage (ring structures, extensive chromosomal breakage/rearrangement precluding precise quantitation) for 50 scored metaphases. ***P < .01 by χ2 test.