ald1/aldC3 females show 8.2% nondisjunction of the X chromosome.
33% of oocytes show disorganisation of the chromosomes in ald1/aldC3 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.