Single nucleotide polymorphisms in wild isolates of Caenorhabditis elegans

Caenorhabditis elegans (isolate N2 from Bristol, UK) is the first animal of which the complete genome sequence was available. We sampled genomic DNA o f natural isolates of C. elegans From four different locations (Australia, Germany, California, and Wisconsin) and found single nucleotide polymorphis ms (SNPs) by comparing with the Bristol strain. SNPs are under-represented in coding regions, and many were found to be third base silent codon mutati ons. We tested 19 additional natural isolates for the presence and distribu tion of SNPs originally found in one of the four strains. Most SNPs are pre sent in isolates from around the globe and thus are older than the latest c ontact between these strains. An exception is formed by an isolate from an island (Hawaii) that contains many unique SNPs, absent in the tested isolat es from the rest of the world, it has been noticed previously that conserve d genes (as defined by homology to genes in Saccharomyces cerevisiae) clust er in the chromosome centers. We round that the SNP frequency outside these regions is 4.5 times higher, supporting the notion of a higher rate of evo lution of genes on the chromosome arms.