Human Chromosome 22
Associated Press Writer
5:15 PM EST; December 1, 1999; For the first time, scientists have mapped virtually an entire human chromosome, one of the chains of molecules that bear the genetic recipe for human life. The achievement announced Wednesday is an important step for the $3 billion Human Genome Project, which is attempting to detail the tens of thousands of genes that carry instructions for everything in a human -- from brain function to hair color to foot size.
"This is the first time that we've had a complete chapter in the human instruction book, and that's pretty amazing," said Francis Collins, who chairs the international project from the National Institutes of Health. "I think this is probably the most important scientific effort that mankind has ever mounted. That includes splitting the atom and going to the moon," he said. In laying out the chemical instructions for life, scientists believe they are in the early stages of revolutionizing the study of human development and medicine.
Already, researchers have begun testing several biological therapies that replace faulty genes or correct their misfirings to make cells work correctly. Such therapies, if they can be made reliable, would bring a more precise way to treat diseases without the sometimes debilitating side effects of conventional drugs. Mutations to genes along the chromosome being mapped contribute to heart defects, immune system disorders, cancers, schizophrenia, and mental retardation.
A draft of the entire genome was expected to be done next Spring, but the milestone announced Wednesday may hasten its completion. The study's details appear in the journal Nature. The human genetic pattern, or genome, is a biological map laying out the sequence of 3 billion pairs of chemicals that make up the DNA in each cell. All human DNA is contained within 23 pairs of chromosomes. What the scientists have done is lay out the order of about 545 of the estimated 700 genes on chromosome 22, which has about 1.1 percent of the genes in the human body.
Chromosome 22 is the second-smallest of the 23 pairs. Scientists took aim at the tiny target because its genes are densely packed and very active in a variety of diseases. About 55 percent of the genes were new to researchers during the study; 45 percent already had been discovered during the Human Genome Project. The Chromosome 22 group, which includes British, American, Japanese, Canadian, and Swedish scientists, could find only 97 percent of the chromosome's genetic material. Scientists said technological limits prevented them from analyzing the remaining 3 percent, which could possibly have as many as 200 genes.
While five government-supported centers and many university labs have already identified about a third of the whole genome, the map of Chromosome 22 is the most complete part so far. "One down, the others to go," said Ian Dunham, a biochemist with the Sanger Centre in Cambridge, England, and lead author of the Nature report. "It's a great relief to have it finished."
Genes are arrayed along chromosomes, the rod-shaped bodies inside the nucleus of a cell. Proteins and other compounds carry out the instructions of genes. Inside the chromosomes, genetic material is linked along tightly coiled strands of the master molecule DNA, which twists like a spiral ladder. Each rung is built with pairs of four chemical bases ordered in different numbers and combinations to form genes. Researchers cautioned that mapping a gene is only an early step in understanding the gene's function and how it might contribute to a particular disease. "Biologists trying to understand, diagnose, treat, and eventually cure human genetic disease will be empowered by our data," said Richard K. Wilson of the Washington University School of Medicine in St. Louis.
The Human Genome Project isn't the only effort to describe the genetic code. The government project is competing with a privately funded effort by Rockville, Maryland-based Celera Genomics, whose work is scheduled for completion by the end of 2001.