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1 Introduction to C. elegans Biology

William B. Wood


Caenorhabditis elegans is a small, free-living soil nematode found commonly in many parts of the world. It feeds primarily on bacteria and reproduces with a life cycle of about 3 days under optimal conditions. The two sexes, hermaphrodites and males, are each about 1 mm in length but differ in appearance as adults, as shown in Figure 1. Hermaphrodites produce both oocytes and sperm and can reproduce by self-fertilization. Males, which arise spontaneously at low frequency, can fertilize hermaphrodites; hermaphrodites cannot fertilize each other.

A hermaphrodite that has not mated lays about 300 eggs during its reproductive life span. Juvenile worms hatch and develop through four stages (commonly referred to as larval stages, although no metamorphosis is involved), punctuated by molts. The mature adult emerging from the fourth molt is fertile for about 4 days and then lives for an additional 10–15 days.

C. elegans is a simple organism, both anatomically and genetically. The adult hermaphrodite has only 959 somatic nuclei, and the adult male has only 1031. The haploid genome size is 8 × 107 nucleotide pairs, about eight times that of the yeast Saccharomyces or one-half that of the fruit fly Drosophila.

C. elegans is easily maintained in the laboratory, where it can be grown on agar plates or in liquid culture with Escherichia coli as a food source (see Methods). It can also be grown axenically in liquid media. Individual animals are conveniently observed and manipulated with the aid of a dissecting microscope,...

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