Strands of Life.

• Author: Bailey, Ronald
• Position: Review

Genome: The Autobiography of a Species in 23 Chapters, by Matt Ridley, New York: HarperCollins, 344 pages, $26.00

The race to find and map all human genes will likely end this year. This is years ahead of the original schedule set by the government-funded Human Genome Project, but stiff competition from the private sector, particularly from Celera Genomics, is now setting the pace of scientific discovery. Celera announced in April that it had completed the sequencing phase of an individual human being's genome and had now begun to assemble the genome segments into their proper order. In other words, Celera has completely read all of the 3.2 billion DNA base pairs that make up a person's genome.

The four DNA bases--adenine, thymine, cytosine, and guanine (ATCG)--combine into 64 three-letter genetic "words" called "codons" that specify a set of 20 amino acids and three "stop" signals. These amino acids, when linked together by reading the DNA that form the various genes, create the thousands of different proteins that make up the human body. These billions of DNA bases are located on 23 pairs of chromosomes which are harbored in nearly every human cell. Such genetic information is really packed into us: If all of the DNA in a single human cell were stretched out, it would reach six feet in length.

By the time you read this, both Celera and the Human Genome Project likely will have completed draft versions of the human genome. What's more, Celera is sequencing the genomes of six men and women of differing ethnic backgrounds to find single nucleotide polymorphisms (SNPs). The SNPs are single-letter variations in genes that differ among people and that determine, among other things, susceptibility to disease and the ability to combat illness. The British Wellcome Trust and various pharmaceutical companies are also searching for SNPs by funding an "SNP Consortium" that plans to identify at least 300,000, and perhaps as many as 1,000,000, of the most common SNPs in human populations.

The speed with which all this is happening is fantastic. Just consider what has happened in half a year. In the December issue of Nature, the Human Genome Project published the genetic sequence of the first human chromosome to be fully mapped, chromosome 22. Chromosome 22 contains 545 known genes and perhaps as many as 1,000 in total. Some 27 human maladies, including one involved with schizophrenia, are linked to changes in genes on chromosome 22.

In March, Celera, working with the Berkeley Drosophila Genome Project, published the complete genome of that most important genetic research animal, the fruit fly Drosophila melanogaster. (Because fruit flies have relatively large, easy-to-see chromosomes and multiply so quickly, scientists have long used them to track genetic processes.) Writing in Science, the researchers identified nearly 14,000 genes, making the fruit fly genome the largest so far sequenced. The fruit fly is also the first insect and the first organism with a central nervous system to be sequenced. (The genomes of several bacteria and the nematode worm C. elegans had been...