Women get more work out of hundreds of genes¹ on the X chromosome² than men do, and that might help explain biological differences between the sexes, a new study says. 

The results imply that women make higher doses of certain proteins than men do, which might play out in gender³ differences in both normal life and disease, researchers said. So far, however, none of the genes identified in the study has been linked to any such observable differences, said senior study author Huntington Willard of Duke University. 

Chromosomes⁴ are the threadlike packages of genes and other DNA⁵ found in cells of the body. People have 24 kinds, numbered 1 through 22 plus the X chromosome and its runty partner, the Y. Women carry two copies of the X chromosome, one inherited from each parent, while men have one X plus one Y chromosome. Long before birth, females permanently⁶ turn off one copy of their X chromosome in each cell, so that like males they operate with just one copy functioning. The choice of which X chromosome is inactivated⁷ is random⁸, an effect made visible in the unusual coats of calico cats. 
But scientists have long known that inactivation⁹ isn’t perfect. Some genes on the inactivated copy continue to function, sending out chemical orders for the cell to manufacture specific proteins. First, they found that 15 percent of the inactivated chromosome’s genes continue to function to some degree. More surprising, Willard said, was what researchers discovered about another 10 percent of the genes. For each, the activity level varied¹⁰ widely from one woman to the next, from zero in some women to varying levels in others.

上一篇：阅读提高：Amazon降雨量受树木影响 下一篇：新东方PETS二级阅读理解题应试指南[1]