Morewright (mwr), a new meiotic mutant of Drosophila melanogaster affecting nonexchange chromosome segregation

A new meiotic mutation, morewright (mwr) was identified by screening for new mutations that act as dominant enhancers of the dosage-sensitive Drosophila melanogaster female meiotic mutant, nodDTW.mwr is a recessive meiotic mutant, specifically impairing the segregation of nonexchange chromosomes. Cytological evidence suggests that the meiotic defect in mwr/mwr females is in homologue recognition because the chromosomes appear to be misaligned on an intact spindle. The mwr mutation was recovered during a screen of random P-element insertions on a chromosome with a single insertion located at 50C. The P-element insertion is a recessive female-sterile mutation. While excision of the P element from the mwr-bearing chromosome partially relieves the female sterility, the excisions retain the dominant nodDTW-enhancing activity. The mwr meiotic phenotype maps very close to the female-sterile P insertion. Thus the mwr locus appears to encode a function required for partner recognition in meiosis, although its relationship to the neighboring female-sterile mutation remains to be elucidated.