The brains of hemizygous larvae have a reduced frequency of anaphase figures, and an increased frequency of polyploid figures and overcondensed chromosomes compared to wild-type. The brains of Klp61F⁰⁶³⁴⁵/Klp61F^urc-4 larvae have a less severe mitotic phenotype. 35.5% of the mitotic spindles in hemizygous larval brain cells are monopolar, 39.6% are bipolar but monastral (only one half-spindle appears to be organised by a centrosome with a focus of γ tubulin) and 16.0% are normal biastral bipolar spindles. 13.3% of the mitotic spindles in Klp61F⁰⁶³⁴⁵/Klp61F^urc-4 larval brain cells are monopolar, 25.8% are bipolar but monastral (only one half-spindle appears to be organised by a centrosome with a focus of γ tubulin) and 60.9% are normal biastral bipolar spindles. The brains and imaginal discs are approximately half normal size in hemizygous larvae, and often similar to wild-type in size and morphology in Klp61F⁰⁶³⁴⁵/Klp61F^urc-4 larvae.

Primary defect is an inability of centrosomes to separate and organise a bipolar spindle. Mitotic figures are highly polyploid consisting of overcondensed chromosomes in apparent monopolar configurations.