Fig. 1.

Chiasmata and crossovers. (A) Diplotene bivalents of Chorthippus brunneus with homologs linked by chiasmata (1). (B) Differential staining of sister chromatids shows that each chiasma is the site of a reciprocal exchange between one sister of each homolog (2). (C and D) Numbers and interference distributions of crossovers (D. melanogaster X chromosome; 3) and chiasmata (Chorthippus L3 bivalent, marked in A; ref. 1). Experimental values (green) and values predicted by the beam/film model (red; details in Fig. 10). [A and B are reproduced with permission from, respectively, ref. 1 (Copyright 1984, Society for Experimental Biology) and ref. 2 (Copyright 1978, Nature Publishing Group).]