Essential Genes * 1. Overview

Understanding the biology of C. elegans relies on identification and analysis of essential genes, genes required for growth to a fertile adult. Approaches for identifying essential genes include several types of classical forward genetic screens, genome-wide RNA interference screens and systematic targeted gene knockout. Based on most estimates made from screening results thus far, from 15–30% of C. elegans genes appear to be essential. Genetic redundancy masks some essential functions and pleiotropy of many essential genes poses a challenge for a full understanding of their functions. Temperature sensitive mutations are valuable tools for studies of essential genes, but our ability to analyze essential genes would benefit from development of new tools for conditional inactivation or activation of specific genes. 1. Overview Understanding the biology of C. elegans relies on identification and analysis of essential genes. An essential gene is defined here as a gene necessary for growth to a fertile adult. Some essential genes were identified fortuitously, but most essential genes have been identified through mutant screens designed specifically to isolate lethal and sterile mutations. Starting with Sydney Brenner's pioneering genetic analysis, many C. elegans geneticists have sought to understand the nature of the genome by estimating the fraction of the genome devoted to essential functions. Based on the frequency of X chromosome lethal mutations, Brenner estimated that the C. elegans genome had about 2000 essential genes (Brenner, 1974). Inclusion of sterile mutations raised this estimate to about 3000,