Figure 6. Meiotic Crossovers in Blm Mutants.

Virgin females with the Blm alleles indicated on the X axis (in trans so the Blm^N1 null allele or, for Blm^N1, Blm^D2) and heterozygous for the net dpp^ho dpy b pr cn chromosome were test crossed and progeny were scored for recessive phenotypes. Graphs show crossover density (cM/Mb) for each genetic interval. (A) Blm^N1 (N1) had a significant reduction in crossovers and an altered distribution, in agreement with a prior study (1). (B) Crossovers were significantly reduced in Blm^ΔCR1 (p < 0.01 by Fisher’s exact test). (C) Blm^ΔCR2 mutants had a modest but statistically significant increase in crossovers (p < 0.01 by Fisher’s exact test. (D) Both Blm^ΔCR1 and Blm^ΔCR2 mutants had significantly higher crossing over than Blm^N1 (p < 0.0001 fof each, Fisher’s exact test for each. n =4031 for wt; 4049 for Blm^ΔCR1; 5088 for Blm^ΔCR2.