The spindle assembly checkpoint is functional in mutant animals; colchicine treatment causes a significant increase in mitotic index in mutant larval neuroblasts but does not significantly increase precocious sister-chromatid separation.

Homozygous and BubR1^D1326N/Df(2R)nap9 males show an elevated frequency of nondisjunction of the sex and fourth chromosomes. The majority of nondisjunction in homozygous males is due to precocious sister-chromatid separation, lagging chromosomes and mis-division at anaphase I and metaphase II.

Homozygous females show an elevated frequency of nondisjunction of the sex and fourth chromosomes. The majority of chromosome nondisjunction in homozygous females appears to be the consequence of a failure to separate properly at meiosis II. The total frequency of meiotic exchange of homozygous females is little if at all affected compared to wild type. However, there are subtle, but highly reproducible, effects on the distribution of exchanges. There is a slight increase in the frequency of non-exchange and a corresponding decrease in the frequency of double crossover on the X chromosome. There is a slight increase in the frequency of crossing over between the pericentric markers st and p on the third chromosome, and a corresponding, but equally weak, reduction in the frequency of crossing over in more distal intervals. There is also an increase in the frequency of non-exchange tetrads and a decrease in the frequency of triple crossover tetrads on the autosomes. Homozygous and BubR1^D1326N/BubR1^Rev1 females show elevated frequencies of exchange in the pericentromeric heterochromatin of the X chromosome.

Homozygous males are fertile, but their progeny show paternal chromosome loss (loss rate of paternal chromosome 4 is 7%). The timing of the chromosome loss appears to be meiotic, based on the observation of micro- and/or macro-nuclei in onion-stage spermatids.