2 Genetics

Abstract

I. INTRODUCTION
As discussed in Chapter 1, the philosophy behind much Caenorhabditis elegans research is that the analysis of mutants by a variety of methods will lead to a better understanding of animal development and behavior. The choice of C. elegans as an experimental organism is thus based, in part, on its tractability for genetic analysis. The purpose of this chapter is to review the current status of the genetics of C. elegans. The discussion of identification and characterization of mutants will cite specific examples primarily for the purpose of illustrating general genetic approaches that have been used; other chapters will focus more directly on specific aspects of C. elegans biology. This chapter also reviews what is known about genome organization (other than at the DNA level, which will be reviewed in Chapter 3) and about chromosomal structure and stability. The system of genetic nomenclature for C. elegans (Horvitz et al. 1979) is discussed in Appendix 4.

II. GENOME ORGANIZATION
A. Diploid Chromosomal Complements
Using Feulgen staining and light microscopy, Nigon (1949a) showed that wild-type C. elegans hermaphrodites contain five pairs of autosomes and one pair of X chromosomes and that males contain five pairs of autosomes and a single X chromosome. Fluorescent dyes such as Hoechst 33258 have been used subsequently for viewing both meiotic (Herman et al. 1976) and mitotic (Albertson and Thomson 1982; Ellis and Horvitz 1986) chromosomes by fluorescence microscopy (Figs. 1 and 2). The chromosomes of oocytes at diakinesis are highly condensed, and the six...