Fig. 3. Mutations in east cause nondisjunction (ND) of achiasmate X-chromosomes in female meiosis. Females carrying different X-chromosomes over the FM7c balancer were crossed with yw males. The bar chart compares the rates of ND of X-chromosomes from wt (CS), the viable east insertion allele ETX3, the viable revertant P86 and six lethal reversion alleles (Wasser and Chia, 2000). To determine frequencies of ND, the numbers of nullo-X (yw males) and diplo-X (w⁺/FM7c) exceptional offspring were scored. The original insertion line ETX3 shows normal segregation, whereas some of the lethal alleles show ND rates of up to 20%. Note that the partial deletion east^hop-7 is associated with more than 20x higher frequency of ND than the complete deletion east^hop-1 of the east transcription unit. n, total number of flies scored.