Gene number. What if there are only 30,000 human genes?

The confirmation that there might be fewer than 30,000 protein-coding genes in the human genome is one of the key results of the monumental work presented in this issue of Science by Venter et al. (1). That a mere one-third increase in gene numbers could be enough to progress from a rather unsophisticated nematode [Caenorhabditis elegans, with about 20,000 genes (2)] to humans (and other mammals) is certainly quite provocative and will undoubtedly trigger scientific, philosophical, ethical, and religious questions throughout the beginning of this new century. By the same token, humans appear only five times as complex as a bacterium like Pseudomonas aeruginosa (3). Although a significant uncertainty is still attached to this low number (see below), it was not totally unexpected, after the downward trend initiated by the analysis of the first two complete human chromosomes (4, 5), as well as two independent statistical studies (6, 7), and the unexpectedly low (14,000) Drosophila gene number (8).