ald¹/ald^C3 females show 8.2% nondisjunction of the X chromosome.

33% of oocytes show disorganisation of the chromosomes in ald¹/ald^C3 females. The oocytes also show spindle defects; 10% have frayed spindles, 14% of spindles are monopolar and 5% lack tapering at the pole.

Oocytes from ald¹/Df(3R)AN6 mutant females enter anaphase prematurely. ald¹/Df(3R)AN6 mutant females do not appear to reach a stable metaphase arrest. Shortly after the spindle forms the chromatin begins to separate into separate masses. This division is not always complete, and can appear aberrant. In some oocytes, the chromatin mass elongates and appears partially split, but remains connected by thin threads of DNA, or large DNA masses can even move back and forth across the spindle.

ald¹/Df(3R)AN6 mutants undergo premature separation in all oocytes.

Oocytes from ald¹ homozygotes enter anaphase prematurely. ald¹ mutant females do not appear to reach a stable metaphase arrest

ald¹ homozygotes undergo separation in nine out of 21 oocytes.

ald¹ mutants show segregational defects for achiasmate homologs. The frequency of achiasmate X chromosome nondisjunction is increased more than 20-fold in FM7a/X; ald¹ females, compared to FM7a/X; ald¹/+ females. The frequency of nondisjunction is even greater (>70-fold higher than FM7a/X; ald¹/+ females) in FM7a/X; ald¹/Df(3R)ED5780 females. FM7a/X; ald¹ and FM7a/X; ald¹/Df(3R)ED5780 mutants also show an increased frequency of 4th chromosome nondisjunction, although this frequency is less than half that of the X chromosome. Cytological analysis shows that the X and 4th chromosome nondisjunction is due to a defective alignment of the achiasmate chromosome pairs at the metaphase plate. ald¹ neuroblasts exhibit a failure of the meiotic spindle checkpoint. Following treatment with colchicine, the checkpoint of wild-type neuroblasts is activated and cells arrest in metaphase. In contrast, 20% of ald¹ neuroblasts and ~5% of ald¹/+ neuroblasts fail to arrest, as shown by precocious chromatid separation. FM7a/X; ald¹ females show a relatively low level of chiasmate X chromosome nondisjunction (5.5% higher than FM7a/X; ald¹/+ females). This frequency is higher (~20%) in FM7a/X; ald¹/Df(3R)ED5780 females. ald¹ and ald¹/Df(3R)ED5780 oocytes have a defect in the maintenance of chiasmate connections between autosomal arms at metaphase I, leading to precocious autosomal separation. Defective ald¹ metaphase plates either display two pairs of autosomes that are fully separated by wispy threads of chromatin, or a complete separation of the autosomes that creates anaphase-like figures.

Homozygous females display elevated levels of nondisjunction of X and fourth chromosomes (9.5 and 6.0% respectively); double exceptions are predominantly XX;0 and 0;44, products expected from nonhomologous disjunction; behavior of large autosomes nearly normal. Exchange frequencies normal and sex-chromosome exchange tetrads contribute to exceptional products.