英语听力文摘 English Digest 712 遗传错误与大脑理论的秘密（在线收听）

Genetic Error and the Big Brain Theory

When cells divide to create copies of themselves or to make sperm and eggs, there is always a chance of genetic error. Gene duplication, when a regular gene is copied twice, is one of those mishaps.

Gene duplication is usually detrimental and can lead to deformation and death if not caught by the cell’s repair machinery. But in rare instances, it may also be evolutionarily important.

Brain Matters

Scientists researching genes important in brain development believe they have found duplication errors that reveal how the human brain increased in size during evolutionary history. While studying SRGAP2, a gene linked to epileptic seizures, scientists found that the gene had not only duplicated once, but a number of times throughout human lineage.

Analysis of the SRGAP2 genes determined that duplications occurred 3.4 and 2.4 million years ago, during which time chimp?like ancestors were evolving into the first pre?humans and human?like ancestors.

Mutant Mice

To test the function of the duplicated genes, scientists inserted human copies into mice. The mice didn’t grow larger brains, but their brain cells looked more like human cells with thicker, longer and more numerous spines to connect with other neurons. The neurons also grew more quickly, suggesting they could migrate farther during development and enable the brain to become larger.

About 30 genes have undergone gene duplication since humans and chimps diverged from a common ancestor about six million years ago. Many of these genes control brain development. Researchers suspect that gene duplication is the key to unlocking the mysteries surrounding human brain evolution.

遗传错误与大脑理论的秘密

当细胞分裂产生自己的复制品或制造精子和卵子时，总有可能发生遗传错误。当一个普通基因被复制两次时，基因复制就是其中的一个不幸。

基因复制通常是有害的，如果不被细胞的修复机制捕获，会导致变形和死亡。但在极少数情况下，它可能在进化上也很重要。

大脑问题

研究大脑发育中重要基因的科学家认为，他们发现了重复错误，揭示了人类大脑在进化史中的大小是如何增加的。在研究与癫痫发作相关的基因SRGAP2时，科学家发现该基因不仅复制了一次，而且在整个人类谱系中复制了多次。

对SRGAP2基因的分析表明，复制发生在340万年和240万年前，黑猩猩在哪一时期？就像祖先进化成第一个祖先？人类和人类？就像祖先一样。

突变小鼠

为了测试复制基因的功能，科学家将人类复制品插入小鼠体内。这些小鼠的大脑并没有长得更大，但它们的脑细胞看起来更像人类的细胞，具有更厚、更长和更多的棘，可以与其他神经元连接。神经元也生长得更快，这表明它们在发育过程中可以迁移得更远，从而使大脑变得更大。

自从大约600万年前人类和黑猩猩从一个共同的祖先分化出来以来，大约有30个基因经历了基因复制。其中许多基因控制着大脑的发育。研究人员怀疑，基因复制是解开人类大脑进化之谜的关键。