Mitotic defects and chromosome instability in strain deleted for brc1. (A) Strategy for creating a null allele of brc1. See MATERIALS AND METHODS for details. (B) UV-C survival curve for wild-type (□) and brc1::ura4 (●). (C) Ionizing radiation survival curve for wild-type (□) and brc1::ura4 (●). (D) Rates of loss of artificial chromosome 10 per generation. Data are expressed as a percentage of total colonies and are corrected for loss at generation zero. Values are wild-type, 0.005; rad18-74, 0.080; brc1::ura4, 0.997; rad18-X, 0.368. (E) DAPI and phase-contrast image of exponentially growing brc1::ura4 cells. Note variability in cell length and mis-segregated chromosomes (top left). Bar, 20 μm. (F–J) Examples of mitotic abnormalities of brc1::ura4. Bars, 10 μm. (F) Nuclear fragmentation and mis-segregation. (G) Stretching of chromosomes along division axis and bisection by septum. (H) Bisection of nucleus by septum and hypercondensation. (I) Hypercondensation and mis-segregation. (J) Fragmentation (above) and incomplete segregation of chromosomes (below left).