Clonal screens to find modifiers of partially penetrant phenotypes in C. elegans

Unbiased genetic screens are an excellent way to discover novel genes involved in specific biological processes in vivo. Modifier screens, whether to suppress or enhance a phenotype, are a powerful way to find proteins that modulate biological processes responsible for specific phenotypes. However, modification of phenotypes that are only partially penetrant, which is often the case, are often extremely difficult to screen this way in a traditional F2 or non-clonal genetic screen. Here we describe an F3 or clonal screen in the nematode Caenorhabditis elegans to search for genes that modify partially penetrant phenotypes. Specifically we describe a screen to search for modifiers of genes that cause defects in migration of a specific developmentally regulated cell, the distal tip cell.