Heterochromatic pairing is nearly normal during meiosis. In prophase I in <10% of mutant oocytes altered pairing of X and FM7a occurs such that two large blocks of X-linked 359bp satellite are separated but the small proximal block on FM7a is paired with one of the large blocks. In metaphase oocytes the non-exchange X chromosomes often remain conjoined as they move away from the plate, rather than separating.

Dominant meiotic mutant that affects distributive pairing; disrupts meiotic segregation of non-exchange chromosomes in females. Has no effect on the frequency of exchange. Loss of function mutation at a dosage sensitive locus; Axs⁺ duplication can rescue mutation in trans. Specific to female meiosis. In Axs^D/Axs^D/Y females, X-chromosomes nondisjunction is accompanied by random disjunction of the Y rather than directed disjunction from the X's as observed in +/+/Y females. Axs^D homozygotes increase X nondisjunction many-fold; parallel but lesser effects observed on autosomal disjunction. Specifically disrupts the segregation of achiasmate homologs. Frequency of nondisjunction of the obligately achiasmate fourth chromosome is also increased, but only in the presence of high levels of X chromosome nondisjunction.