Segregation patterns of chromosomes. (A) Normal meiosis produces four haploid products. Aberrant segregation may be monitored using centromere linked markers. Diploid spores resulting from MI nondisjunction (B) and precocious separation of sister chromatids (D) are predominantly heterozygous for the centromere, whereas those arising by MII nondisjunction (C) are homozygous for the centromere. (E) Diploid spore colonies were genotyped for heteroallelic marker loci tightly linked to each of the three centromeres (lys1, chromosome I; tps13, chromosome II; and ade6, chromosome III). Each value is based upon genotyping between 50 and 80 diploid spore colonies and the mean ± standard deviation for all three chromosomes in each mutant is indicated (black bars). The data were from crosses of strains: WSP1807 × WSP1216; WSP1825 × WSP1884; and WSP1670 × WSP1809.