© 2001 by Oxford University Press
Journal of the National Cancer Institute, Vol. 93, No. 7, 493,
April 4, 2001
© 2001 Oxford University Press
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Draft Human Genome Sequence Yields Several Surprises
Perhaps the biggest surprise produced by the draft sequence of the human genome is that humans have about the same numbers of genes as fruit flies, flowering plants, and worms—30,000 to 40,000. However, humans have a lot more multifunctional proteins.
Most of the subunits that make up human proteins are the same as those in other organisms, said Eric Lander, Ph.D., of the Whitehead Institute for Biomedical Research in Cambridge, Mass., a leader in the international effort to sequence the human genome. In humans, though, these subunits are assembled more creatively and with more variety than in other organisms. The result is that we have more immune system proteins, structural proteins, specialized epithelial proteins, and growth factors. Human complexity seems to lie in the diversity of proteins, not genes.
Another surprise is the extent of repeat DNA. With the genes accounting for only 1.5% of the human genome, Lander said that more than half of the remaining DNA consists of very long stretches of repeated sequences. In addition, he believes that at least another 25% is also repeat DNA.
"Each repeat was born on some particular day and was a copy of some active element," Lander said at the January Oncogenomics Conference jointly sponsored by Nature Genetics and the American Association for Cancer Research. It turns out that most repeat sequences in the human genome are millions of years old. (This is in contrast to the fly, for example which has very young repeat elements.) Apparently, said Lander, the human genome does not engage in active housecleaning. A piece of useless DNA stays in the genome for hundreds of millions of years before its discarded.
"What that means is that the human genome is a spectacular fossil record of the last billion years of evolution," Lander said. "If we pay attention, there is no end to what we can learn."
Another interesting finding came from looking at the variation in DNA from one person to another. The researchers concluded that humans do not differ a lot. Lander said that the DNA of any two people on this planet is 99.9% identical. Put another way, any given village in the world represents 70% of all the variation found in the human genome.
With this sequence now publicly available, scientists can go to several Web sites to search for the sequence of any of the human chromosomes, as well as their associated genes and protein products (see box above). And in addition to the human, genome sequences have been completed for yeast, the small worm Caenorhabditis elegans, the mustard weed Arabidopsis thaliana, the fruit fly Drosophila, 600 viruses, and 30 bacteria. The complete genomes for the mouse, the rat, the zebrafish, two pufferfishes, and rice are in the pipeline.
Where to Find the Human Genome
Some examples:
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