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Male Chromosome Not
"Genomic Junkyard"

NEW YORK (Reuters Health) - As part of the Human Genome Project, scientists have constructed the map of the Y chromosome--the stocky chunk of DNA that makes men look and act like men--and it's not what they expected. In fact, it is more interesting than once thought, according to one of the researchers involved in the mapping, Dr. David C. Page.

In an interview with Reuters Health, Page, of the Whitehead Institute at the Massachusetts Institute of Technology (MIT) in Cambridge, said that for many years the Y chromosome was considered to be a ``genomic junkyard'' that contained few, if any, genes. Besides determining a person's sex, scientists generally thought the chromosome was a bit of a wasteland, he said.

But based on the recently constructed map, a better label for the Y chromosome is ``the genome's national park,'' according to Page, who said that the male chromosome contains ``quite amazing features.'' The findings are published in the February 15th issue of the journal Nature, a special issue of the journal with scientists' first look at the completed sequence of the human genome.

The newly constructed map ``provides the foundation for sequencing the chromosome that has historically been very (poorly) understood,'' Page said.

The MIT scientist explained that the Y chromosome differs from other chromosomes in two ways. First, it is only present in one sex (women have two X chromosomes while men have an X and a Y). Second, the chromosome is the only one that does not participate in a process called recombination--a shuffling of the genetic deck that occurs in the making of an embryo.

Because 95% of the chromosome is not involved in recombination, the chromosome has evolved differently than the others over the course of the last 300 million years, Page noted.

One of the interesting features that the mapping of the chromosome revealed was the repetition of large chunks of the chromosome, he said. At first glance, these segments may appear to be ``abandoned debris'' that does not serve any function, but these repeated segments actually carry many genes involved in the production of sperm, which is the chromosome's ``specialty,'' Page pointed out.

``It turns out that the part of maleness that the Y chromosome really has to do with is sperm production,'' he said. He noted that defects in the Y chromosome have been linked to some types of male infertility.

Page added that the map is only a glimpse of what is contained in the Y chromosome. Later in the year, he and his colleagues expect to publish the results of the sequencing of the chromosome, he said.

SOURCE: Nature 2001;409:943-945.

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