Sequencing the human genome has led to some surprising results. For example, we once thought that highly evolved humans would need a great many genes to account for their complexity, and scientists originally estimated the number of human genes to be about 100,000. The draft of the human genome, however, indicates that humans may have only about 30,000 genes, far fewer than originally expected. Indeed, this is only about one-third more than the number of genes found in the lowly roundworm, Caenorhabditis ele-gans (approximately 20,000 genes), and roughly twice the number of genes in the fruit fly Drosophila melanogaster (approximately 14,000 genes). Subsequent estimates have placed the number of human genes closer to 70,000; the true number is unknown as of mid-2002. Scientists have learned that most of the genome does not code for proteins, but rather contains "junk DNA" of no known function. In fact, only a small percentage of human DNA actually encodes a gene.
The complete human genome consists of twenty-two pairs of chromosomes plus the X and Y sex chromosomes. On December 2, 1999, more than 100 scientists working together in laboratories in the United Kingdom, Japan, the United States, Canada, and Sweden announced the first completely sequenced human chromosome, chromosome 22, the smallest of the autosomes. To assure the accuracy of the sequence data, each segment must be sequenced at least ten times.
Thousands of scientists, working in more than 100 laboratories and 19 different countries around the world, have contributed to the Human Genome Project since its inception. Thanks to the development of later generations of high-speed automatic sequencers and supercomputers to handle the enormous amount of data generated, work on the project progressed well ahead of schedule and well under budget, a rare phenomenon in
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