- The Washington Times - Thursday, September 1, 2005

NEW YORK — The human Y chromosome — the DNA chunk that makes a man a man — has lost so many genes over evolutionary time that some scientists have suspected that it might disappear in 10 million years. But a new study says it will stick around.

Researchers found no sign of gene loss over the past 6 million years, suggesting the chromosome is “doing a pretty good job of maintaining itself,” said researcher David Page of the Whitehead Institute for Biomedical Research in Cambridge, Mass.

That agrees with prior mathematical calculations that suggested the rate of gene loss would slow as the chromosome evolved, Mr. Page and study co-authors note in the journal Nature. They say the research clashes with what Mr. Page called the “imminent demise” idea that says the Y chromosome is doomed to extinction.

The Y chromosome appeared 300 million years ago and has eroded since into a dinky chromosome, because it lacks the mechanism other chromosomes have to get rid of damaged DNA. So, mutations have disabled hundreds of its original genes, causing them to be shed as useless. The Y chromosome now contains only 27 genes or families of virtually identical genes.

In 2003, Mr. Page reported that the modern-day Y chromosome has an unusual mechanism to fix about half of its genes and protect them from disappearing. But he said some scientists disagreed with his conclusion. The new paper focuses on a region of the Y chromosome where genes can’t be fixed that way.

Researchers compared the human and chimpanzee versions of this region. Humans and chimps are thought to have been evolving separately for about 6 million years, so scientists reasoned that the comparisons would reveal genes that have become disabled in one species or the other during that time.

They found five such genes on the chimp chromosome but none on the human chromosome.

“It looks like there has been little if any gene loss in our own species’ lineage in the last 6 million years,” Mr. Page said.

That contradicts the idea that the human Y chromosome has continued to lose genes so fast that it will disappear in 10 million years, he said.

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