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让我不爽的一篇阅读，google的各段内容的拼接，大概就是这个样子。问题有几道设在预测和分析上，比较难： Soay sheep living wild on the Scottish island of Hirta come in two colors: light brown and dark brown. Researchers have known that the dark sheep are bigger than the light ones. Extra heft translates into an advantage in winter survival and reproduction. "We would have expected [the dark sheep] to have increased in frequency over a 20-year time series," says Jon Slate of the University of Sheffield in England. Not so, Slate and his collaborators say in the Jan. 18 Science. Biologists have kept records on the Hirta population since 1985, and big dark sheep have not been taking over the population. Analyzing the ups and downs of colors shows that dark-coated sheep are becoming less common. The researchers earlier identified the coat-color gene and discovered that dark was dominant. If a sheep gets the dark-brown variant from one or both parents, it will be dark brown. Only if it gets the light-color variant from both parents will it be light brown. In the new research, reported in Science, they found nearby locations on the genome that affect body size, juvenile survival and reproductive success. They don’t know why these loci, as they are called, have the effects they do. But when the dark-color variant is passed to offspring, it’s accompanied by genes that positively affect body size but negatively affect juvenile survival and reproduction. When the light-colored variant is passed on, genes for smaller body size but better survival and reproduction come along for the ride. That means light-brown sheep, and dark-brown sheep who have the dark-brown gene from only one parent, are more fit. Sheep with dark-brown genes from both parents are less fit, which accounts for their decreasing numbers. Their larger size is not enough to offset the other genetic factors. “If it wasn’t for the body-size gene, they’d be even worse off,” Dr. Slate said. 
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发表于 2009-5-20 19:01:00
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