Magazine article Science News

Two Human Chromosomes Entirely Mapped

Magazine article Science News

Two Human Chromosomes Entirely Mapped

Article excerpt

In two of the earliest major advances in the mammoth international effort to identify and decipher all of the estimated 100,000 human genes, two groups of researchers have taken apart and put back together the smallest human chromosomes: the Y chromosome and chromosome 21.

The exercise have yielded for each chromosome a set of overlapping segments of DNA assembled in the correct order. Scientists expect both of these so-called physical maps to help them find new genes more quickly. They also predict that the map of the Y chromosome will shed new light on human evolution.

Scientists at the Whitehead Institute for Biomedical Research in Cambridge, Mass., constructed the physical map of the Y chromosome. The team, led by David C. Page, began by examining the Y chromosomes of individuals who had inherited only fragments of this rod-shaped structure, which bears the genes that make a male.

By comparing the different-size Y chromosome fragments of 96 such individuals, Page and his colleagues discovered naturally occurring breakpoints that they could use as molecular probes. This comparison also allowed the researchers to organize the probes into the order in which they would occur in an intact Y chromosome.

Page's group then used the probes to isolate long pieces of the Y chromosome from a man who had three extra Y chromosomes, which provided the researchers with an abundance of material for study. By assembling the pieces in the order of the probes, Page and his colleagues reconstructed 98 percent of the part of the Y chromosome that contains genes. They describe their work in two papers in the Oct. 2 SCIENCE.

Douglas Vollrath, a key member of Page's group, says the discovery should speed the Human Genome Project. "Until recently, the most difficult part was finding the DNA that you thought contained a particular gene," says Vollrath. …

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