Screen results and allelic series studied.

The 28 mutant lines (Ws-4 accession) isolated in this study are presented as well as additional alleles (asterisk) obtained in another accession (Col-0). Each of the mutations is presented within its complementation group together with the name of the mutated gene. Chiasma count at metaphase I is provided as well as the nature of the mutation. Full sequence information is provided in Table S1. ** Described in [50], nd: not determined, n: number of cells.