Detailed knowledge of gene expression patterns in simple organisms can provide a solid platform from which to study the regulation of developmental processes in more complex organisms. Reinke et al. supply such a platform by identifying 5629 genes with distinct germline or sex-dependent expression profiles in the nematode worm, and by examining their spatial and temporal expression patterns (see p. 311). Their detailed work makes use of DNA microarrays corresponding to 92% of the predicted genes in the Caenorhabditis elegans genome. By examining gene expression profiles in mutants with defects in germline proliferation or gamete production, and in males and hermaphrodites, the researchers identify most of the worm's germline-expressed and sex-regulated genes. Among other things, their global overview uncovers striking biases in the distribution of these genes in the genome and in the classes of proteins they encode.