(A) The expected (based on Poisson distribution) and observed frequency of E0
X chromosomes in wild type and in Blm mutants. Bars are 95% confidence intervals. ***P <0.0001 based on two-tailed Fisher’s exact test of numbers observed and expected. For a similar analysis of chromosome 2L, please see Figure S3.
(B) Classification of nondisjoined chromosomes. The top schematic represents heterozygous X chromosomes in Blm mutant females. Below are structures of chromosomes recovered in daughters that inherited two maternal X chromosomes. All were meiosis I nondisjunction based on the centromere-linked marker (y+). 33 were non-recombinant; one had a crossover between f and y+ (arbitrarily drawn within the euchromatin). The frequency of non-exchange (E0) X chromosomes among those that failed to disjoin (0.97) is significantly different than among those X chromosomes that disjoined correctly (0.51) (P =0.0005).