听力文摘：冰河世纪动物如何生存

During the last ice age, rapid swings in temperature occurred within decades or less, meaning populations of organisms had to adjust quickly to new environments or face extinction¹.

在最后一个冰河世纪中，温度在数十年甚至更短的时间内迅速变化，这意味着生物种群不得不快速调整来适应新的环境，否则等待它们的只有种族灭绝。

Scientists knew there wasn't time for the genetic³ code to mutate within individuals and spread throughout large populations. So, how did animals respond? Ancient bison preserved in the Canadian arctic have given scientists a clue.

科学家知道那时基因编码没有时间在个体中产生变异并在种群中大范围地传播。那么，动物们是如何应对的？在加拿大北极圈内保留的古代野牛标本给科学家们提供了一些线索。

When genes⁴ were first identified, scientists thought they were hard wired. One gene² made one protein and was unalterable. Today we know the story is much more complex. Part of that complexity⁵ is known as epigenetics, a process by which genes are modified by environmental factors.

第一次识别古代野牛的基因时，科学家们认为它们是固定相连的。一个基因对应一个蛋白质并且无法改变。如今我们知道故事远没有那么简单。其中一部分复杂性来自表观遗传学，它是基因通过环境因素发生改变的过程。

The genetic code stays the same, but certain molecules⁶ attach to the code to prevent specific genes from working or to change how they are expressed. Other molecules can affect the chromosome⁷ and alter the way the DNA⁸ unwinds, affecting how genes work.

基因密码保持不变，但是某个为阻止某个特定基因工作或变更的密码附属分子发生了变化。而其它分子可以通过影响染色体并改变DNA解旋的方式来影响基因的表达。

Extracting DNAScientists examining twenty six thousand year old bison bones looked for evidence of epigenetic changes in extracted DNA. They analyzed⁹ the genetic code for a particular kind of epigenetic change called DNA methylation. They not only found methylations, they found them in locations where they occur in modern cattle. That suggested they weren't due to DNA degradation¹⁰, but were true epigenetic changes.

DNA提取科学家检查了已有26000年历史的古代野牛的骨头，试 图在提取的DNA中找到表观遗传变异的证据。他们分析了一种特定种类的表观变化（被称为DNA甲基化）的基因密码。他们不但找到了甲基化，而且发现它们跟 现代牛群体内发现的位置是一样的。这表明它们不是发生了DNA退化，而是真正的表观遗传变异。

This is just the first step in solving the ice age adaptation puzzle. Scientists plan to gather more DNA samples from animals that lived before and after the dramatic climatic shifts. That way they'll have genetic snapshots to compare. If comparisons prove successful, the next step will be to determine exactly how the epigenetic alterations¹¹ changed the gene expression.

这仅仅是解决冰河世纪适应谜团的第一步。科学家计划在气候剧烈变化前后生存过的动物身上收集更多的DNA样本。如此一来，他们就有更多的基因用来比较。如果比较的结果证明是之前的推断是正确的，那么下一步是确定表观变化是如何影响基因表达的。

1 extinction   

n.熄灭，消亡，消灭，灭绝，绝种

参考例句：

• The plant is now in danger of extinction.这种植物现在有绝种的危险。
• The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。

2 gene   

n.遗传因子，基因

参考例句：

• A single gene may have many effects.单一基因可能具有很多种效应。
• The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。

3 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

4 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

5 complexity   

n.复杂(性)，复杂的事物

参考例句：

• Only now did he understand the full complexity of the problem.直到现在他才明白这一问题的全部复杂性。
• The complexity of the road map puzzled me.错综复杂的公路图把我搞糊涂了。

6 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

7 chromosome   

n.染色体

参考例句：

• Chromosome material with exhibits of such behaviour is called heterochromatin.表现这种现象的染色体物质叫做异染色质。
• A segment of the chromosome may become lost,resulting in a deletion.染色体的一个片段可能会丢失，结果产生染色体的缺失。

8 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

9 analyzed   

v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析

参考例句：

• The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
• The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程，因为对他来说，爱是个不可分析的迷。 来自《简明英汉词典》

10 degradation   

n.降级；低落；退化；陵削；降解；衰变

参考例句：

• There are serious problems of land degradation in some arid zones.在一些干旱地带存在严重的土地退化问题。
• Gambling is always coupled with degradation.赌博总是与堕落相联系。

11 alterations   

n.改动( alteration的名词复数 )；更改；变化；改变

参考例句：

• Any alterations should be written in neatly to the left side. 改动部分应书写清晰，插在正文的左侧。 来自《简明英汉词典》
• Gene mutations are alterations in the DNA code. 基因突变是指DNA 密码的改变。 来自《简明英汉词典》