mei-9^b/mei-9^A2 females show 31% X chromosome nondisjunction, compared to 0.33% in wild-type females. mei-9^b/mei-9^A2 larvae are hypersensitive to ultraviolet light and nitrogen mustard.

Recombination in females is reduced to 16% of control levels. Chiasma frequency greatly reduced. Stage 14 oocytes can finish both meiotic divisions without metaphase arrest. Rare normal metaphase figures indicate that even one chiasma is sufficient to ensure metaphase arrest.

Increases the frequency of X chromosome non-disjunctions in nod^a mutants.

Homozygotes have an increased frequency of X chromosome non-disjunction.

Reduces meiotic exchange uniformly throughout the euchromatin. Deleted chromatids are occasionally recovered.

Meiotic crossing-over is reduced by a factor of 1/6 in homozygous females. Meiotic crossing-over is reduced by a factor of 1/12 in mei-9^a/mei-9^b females. The frequency of gene conversion at the ry locus is unaffected in homozygous or mei-9^a/mei-9^b females. Post-meiotic segregation events, manifested as mosaic progeny, are produced at high frequency in homozygous and mei-9^a/mei-9^b females.

Homozygotes and hemizygotes show a higher frequency of spontaneous chromosome aberrations in neuroblast metaphases than wild-type larvae. The ratio of chromatid breaks to isochromatid breaks is 5.9-8.6. Approximately half of the breaks are heterochromatic and half are euchromatic. The breaks appear to be randomly distributed among the chromosomes. Breaks are 1.4-1.6 times more frequent in females than in males.

mutagen sensitive reduces exchange mitotic instability