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Finally found this, share with you all:
From: https://forum.chasedream.com/thread-389352-1-1.html
"记住了是Soey sheep ，刚才google到了，来自New York Times
可以确定是同一篇，以及中文译文。
http://www.nytimes.com/2008/01/22/science/22obshee.html?_r=1
http://www.gengrid.com/node/106
The Soay sheep of St. Kilda, a group of small Scottish islands, have been living free and unfettered for millennia（考试中此处有注释）. While these primitive sheep are still unmanaged, detailed records have been kept on them for the past 20 years. That makes St. Kilda a kind of natural evolutionary experiment, an island-scale Petri dish where sheep, not fruit flies, are the subjects.
Soays come in two colors: light brown and dark brown. The dark-brown sheep are bigger, and evolutionarily speaking, bigger should be better — big animals are more fit and more likely to survive.（此处有题，问该句作用，选的是：提出一个basic principles 而引出soay sheep的现象为什么会引起科学家的好奇） So over time, the frequency of dark-brown sheep in the population should be increasing. But the St. Kilda records show that the opposite is true.
Now a team of scientists led by Jon Slate, an evolutionary geneticist at the University of Sheffield in England, has discovered why. “It comes down to where on the genome the coat-color gene sits,” Dr. Slate said. “It just happens to sit next to this fitness gene.”
The researchers earlier identified the coat-color gene and discovered that dark was dominant（我们高中学过的显性基因）. 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.（只要从父母的任何一方遗传得到一个深棕色的等位基因，它就是深棕色的；只有同时从父母身上都遗传得到浅棕色的等位基因，才会出现浅棕色的症状。这句话一定要注意，其中一题问，如果是一只light color的羊，我们能得出什么结论，选的是，这只羊不会有dark基因。
即决定样颜色性状的是A，a两种基因，AA Aa都是深色的只有aa才是浅色的。因而浅色羊不会含有A）
即决定样颜色性状的是A，a两种基因，AA Aa都是深色的只有aa才是浅色的。因而浅色羊不会含有A）
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.
野生索艾羊(Soay Sheep)已在苏格兰的圣基达岛(St Kilda Is.)上与世隔绝、毫无拘束地生活了上千年的时间。处于这种环境下的索艾羊是研究自然进化的绝佳材料--圣基达岛就像一个巨大的培养皿，而其中的索艾羊就像果蝇一样。
有两种颜色的索艾羊：浅棕色和深棕色。深棕色的索艾羊个体更大，从进化的角度来说，形体越大越好--大型动物的适应性更好，更有可能生存下去。因此随着时间的推移，索艾羊种群中深棕色的羊比例应该越来越大。但过去20年记录显示的结果却完全相反。
英国布里斯托尔大学（University of Bristol）Jon Slate领导的的研究小组发现了其中的原因。 Slate博士说，这是由于羊毛颜色基因位点附近的基因决定的，这个基因叫做适应性基因（fitness gene）。
较早前研究人员已鉴定出羊毛的颜色基因，并发现深棕色的为显性。只要从父母的任何一方遗传得到一个深棕色的等位基因，它就是深棕色的；只有同时从父母身上都遗传得到浅棕色的等位基因，才会出现浅棕色的症状。
在这项新研究中，他们发现在基因组相邻的基因位点，分别会影响形体的大小，小羊的存活率和生殖的成功与否。他们不知道为什么这些位点会有这种作用。当深棕色的等位基因遗传给子代时，同时也遗传正向影响形体大小的基因，但也遗传着负向影响小羊存活率和生殖能力的基因。当浅棕色的特征遗传给索艾羊时，索艾羊同时也获得更小的形体的基因，以及更好存活和生殖的基因。
这意味着，浅棕色的索艾羊和仅有一份深棕色基因的深棕色索艾羊，适应性要更强。这就是浅棕色索艾羊数量增多的原因。更大的形体不足以抵消其它的遗传因素。Slate博士表示，“如果不是形体大小的基因，那它们就更糟糕。” |
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发表于 2017-12-19 11:08:08
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