Genetic dissection of developmental pathways

A major tool of developmental geneticists is the ordering of genes in functional pathways. In this chapter, we explain the logic behind constructing pathways, starting from the knowledge of the relevant phenotypes associated with the genes of interest, assuming that careful analysis of the phenotype has been carried out. We discuss the construction and interpretation of phenotypes of double mutants, screening for and analysis of extragenic suppressors, as well as issues regarding complex pathways and genetic redundancy. Avery and Wasserman (1992) have provided a brief theoretical discussion of epistasis analysis; here we explain the more practical aspects of how models of developmental pathways are built in C. elegans.