Structure, Function and Evolution of The Nematode Genome

In the past few years, an increasing number of draft genome sequences of multiple free-living and parasitic nematodes have been published. Although nematode genomes vary in size within an order of magnitude, compared with mammalian genomes, they are all very small. Nevertheless, nematodes possess only marginally fewer genes than mammals do. Nematode genomes are very compact and therefore form a highly attractive system for comparative studies of genome structure and evolution. Strikingly, approximately one-third of the genes in every sequenced nematode genome has no recognisable homologues outside their genus. One observes high rates of gene lossesand gains, amongthemnumerous examples of gene acquisition by horizontal gene transfer. Not only does the ‘gene for parasitism’ not exist, but also there appear to be no common genomic characteristics of parasitic nematode genomes which would distinguish them from genomes of free-living nematodes.