Courtesy of Douglas K. Bishop and Denise Zickler, © Elsevier Science
The double-strand-break repair model (A) posits that during meiotic prophase I, crossovers (COs) and noncrossovers (NCOs) begin with a double-strand break (DSB) of a DNA helix. Cleavage of a structure known as the Holliday junction (HJ) ultimately generates both COs and NCOs. A newer model (B) proposes that COs still arise from HJs (right) but that NCOs come from a pathway called synthesis-dependent strand annealing (left) that does not involve HJs. (Reprinted from
Thousands of geneticists owe their livelihoods to meiotic recombination, that diversity-promoting process during egg and sperm development when homologous chromosomes from Mom and Dad swap pieces. But recombination is so dauntingly complex that only a few geneticists have dared to propose models describing its underlying mechanics. For decades, cytology and genetic analysis provided data to test these hypotheses. Now molecular and biochemical tools ...
