Heterozygotes are WT and segregate WT, Stu and DpyUncs. e1457 is a strong loss-of-function or null allele. Molecular lesion: G to E at position 40. DNA replication continues in the absence of mitosis. Mutants enter mitotis at the normal time and form bipolar spindles, but fail chromosome alignment at the metaphase plate, sister chromatid separation and cytokinesis.