The present work provides a clear example of the value of a chemical genetics approach, as the infertility and dwarf phenotype of a homozygous mekk1 mutation (Ichimura et al., 2006; Nakagami et al., 2006; Suarez-Rodriguez et al., 2007) would have precluded the identification of MEKK1 as a component of the l–Glu signalling pathway in a conventional forward genetics screen. Here, MAP3K1 is linked to Infertility.