Numbers of MLH1 foci per chromosome.

Pachytene spermatocyte spreads were immunostained for SYCP3 and MLH1. Autosomal bivalents in each spread were rank-ordered according to SC length from 1 (largest) to 19 (smallest), then divided into groups of similarly sized chromosomes. P-values are shown for log-likelihood (G) tests comparing each size group from Spo11+/−Atm−/− cells to the same size group from Spo11+/− cells, not including the zero-focus class. (Note that bivalents with zero MLH1 foci are ambiguous because foci are transient.)