Figure 2.

(A–E) Chromosome pairing and recombination events. (A) Quadrivalent with partner switch between centromere and centromere-proximal locus. (B) Quadrivalent with partner switch between loci. (C and D) Quadrivalents with partner switch outside the two regions in A and B, effectively equivalent to E. (E) Two bivalents (no partner switch). D, centromere-distal locus; P, centromere-proximal locus; open circles, centromeres. X’s denote possible recombination events (two events per X). Shaded text and arrows describe the order of recombination events taken account of in the computer program. Curly brackets indicate that chromatid partner choice is not independent. Annotation of recombination events is implicitly the same in C–E.