Viability is strongly reduced in homozygotes (27%) and in Dp1^15.1/Df(2R)PC4 flies (8%). The reduced viability affects females more dramatically as 70% of escapers are males. Male escapers are fertile, but female escapers are sterile and have abnormal ovaries; the ovarioles are often undeveloped and contain egg chambers that are often fused and contain an irregular number of cells. Homozygous female escapers do produce some eggs, but they fail to develop, even when fertilised by wild-type males. The embryos derived from the homozygous females die at all stages of embryonic development and show a broad range of defects. In all cases, these embryos have altered chromosome condensation. Two main types of nuclear condensation defect are seen. Firstly, before germ band retraction, nuclei are significantly undercondensed compared to those in embryos derived from wild-type females. There is considerable variation in nuclear size, with some nuclei being much larger than normal. In some cases, undercondensed chromatin is visible in large clumps that have the appearance of fused nuclei. Secondly, after germ band retraction, some embryos have strongly overcondensed nuclei. Embryos with both undercondensed and overcondensed nuclear material are seen. Chromatin fragmentation is also observed. Embryos derived from homozygous females show a high frequency of segregation defects during mitosis; lagging chromatin bridges are often seen at anaphase, and at telophase, elongated chromatin fibres are seen to connect segregating nuclei and some nuclei have a dumb-bell shape (reflecting delayed chromatin material that reaches the poles late in telophase). In late embryos showing undercondensed nuclei, the frequency of aberrant mitoses can be as high as 80%, but no mitoses are detected in embryos showing overcondensed nuclei. The transmission of the non-essential Dp(1;f)1187 chromosome is reduced in Dp1^15.1 males.