3 The Genome

Abstract

I. INTRODUCTION
The physical basis of the Caenorhabditis elegans genetic system is a genome of 8 × 10⁷ base pairs of DNA. This DNA is organized into six nuclear chromosomes plus the mitochondrial chromosome. The small size of the genome, only 20 times that of Escherichia coli and half that of Drosophila, is consistent with the small number of genes in C. elegans, as measured by genetic means. The ratio of the number of base pairs of DNA to the estimated number of genetic loci, about 20,000, is similar to the value for Drosophila and appears to be typical for eukaryotic organisms generally. The C. elegans genome is typical in other respects as well. The sequences that it comprises are, in general, identically arranged in every cell. They consist of both unique sequences and repeated sequences. As in other eukaryotes, the repetitive component is a complex class made up of repeated genes, transposable elements, and diverse, short repeated sequences whose origin and function are unknown. Repeated sequences and unique sequences are intermingled throughout the DNA.

A central aim of C. elegans research is to understand how the information that specifies the organism is encoded in the genome and how this encoded information is read out in a temporally and spatially coordinated fashion during the life cycle. A primary aim of research on the genome, therefore, has been to provide means for isolating genes so that gene products may be identified and gene activity studied at the biochemical level. The small...