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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 it might disappear in 10 million years. But a new study says it’ll 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, Page and study co-authors note in Thursday’s issue of the journal Nature. And, they say, it clashes with what Page called the "imminent demise" idea that says the Y chromosome is doomed to extinction.
The Y appeared 300 million years ago and has since eroded 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 now contains only 27 genes or families of virtually identical genes.
In 2003, Page reported that the modern-day Y 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 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, an imbalance Page called surprising. "It looks like there has been little if any gene loss in our own species lineage in the last 6 million years," Page said. That contradicts the idea that the human Y chromosome has continued to lose genes so fast it’ll disappear in 10 million years, he said. "I think we can with confidence dismiss … the ’imminent demise’ theory," Page said.
Jennifer A. Marshall Graves of the Australian National University in Canberra, a gene researcher who argues for eventual extinction of the Y chromosome, called Page’s work "beautiful" but said it didn’t shake her conviction that the Y is doomed.
The only real question is when, not if, the Y chromosome disappears, she said. "It could be a lot shorter than 10 million years, but it could be a lot longer," she said.
The Y chromosome has already disappeared in some other animals, and "there’s no reason to expect it can’t happen to humans," she said. If it happened in people, some other chromosome would probably take over the sex-determining role of the Y, she said.
The word "dinky" ( line 1, paragraph 4) most probably means
[A] dirty. [B] tricky. [C] mai-functional. [D] defective.

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The text does not directly say, but implies that Kissinger [A] suffered a series of defeats while being in office. [B] significantly altered the direction of international relationships. [C] was unsuccessful in bringing about peace in the Middle East. [D] played a more important role than the president during the Nixon administration.

Another major work was the Strategic Arms Limitation Talk. Though his term in office passed with the treaty unsigned, Kissinger left a draft of the treaty to which the Russians had already agreed. The SALT treaty spelled out a one-tenth reduction in nuclear arms, a major accomplishment by any standard, even if one does not consider all the other conditions and limitations included in the treaty.
Even though he successfully helped bring an end to the Vietnam War, Kissinger’s final days in office were affected, as was the entire executive branch in one way or another, by the scandals of the Nixon White House. Kissinger’s critics point to his role in placing wiretaps on the phones of reporters and officials and to what they consider his "high-handed" approach to setting foreign policy. But Kissinger, during the last few months of the Nixon presidency, limited the effects of American domestic problems on our foreign policy. He continued talks in the Middle East. He continued close contact with the Soviet Union.
History will decide in the final view, as Kissinger--and many presidents--often said, on the value of his service. Whatever they decide, whether his actions are finally to be considered wise or foolish, he had a personal vision that will be difficult to match. (459 words)Notes: work out 制定。spell out 清楚地说明。wiretap 窃听(电话)。scandal 丑闻。
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