VOA慢速英语--研究发现:同卵双胞胎的基因也不完全一样

A new study suggests that identical twins are not exactly the same genetically². Identical twins are two babies that come from the same fertilized³ egg.

Scientists in Iceland examined DNA⁴ from 387 pairs of identical twins, their parents, children, husbands or wives.

The examinations led the team to find "early mutations that separate identical twins," lead researcher and geneticist Kari Stefansson said. He is a professor at the University of Iceland and founder⁶ of the company deCODE⁷ genetics.

Mutations are small changes in DNA that can happen when a cell divides in an attempt to copy itself. These small changes can influence a person's physical appearance or control a person's ability to fight a disease.

The newly-discovered mutations show that identical twins do have genetic¹ differences, the researchers said. The results were recently published in Nature Genetics.

On average, identical twins have 5.2 of these early genetic differences, the researchers found. But about 15 percent of identical twin pairs have more than that. Some might have as many as 100 genetic differences, Stefansson said.

These differences represent a small part of each twin's genetic material. But they could influence why one twin is taller or why one is at greater risk for some cancers than the other.

In the past, many researchers believed physical differences seen in identical twins were related mostly to environmental influences, such as nutrition or lifestyle behaviors.

Jan Dumanski is a geneticist at Sweden's Uppsala University. He was not involved in the study. He praised the findings as "a clear and important contribution" to medical research.

"The implication is that we have to be very careful when we are using twins as a model" for examining the influences of genetics or the environment, Dumanski said.

A 2008 paper in The American Journal of Human Genetics found some genetic differences between identical twins. The new study, however, goes beyond earlier work by including the DNA of parents, children, husbands and wives of identical twins.

Studying family members permitted the researchers to examine when genetic mutations happened in two different kinds of cells: those present in only one individual and those passed on to the person's children.

Stefansson said his team found twins where a mutation⁵ is present in all cells of the body of one twin, but not in the other twin at all. However, "sometimes the second twin may show the mutation in some cells, but not all cells," he added.

The researchers said they also found mutations that came about before the developing embryo⁸ split in two.

Nancy Segal is a psychologist who studies twins at California State University, Fullerton. She was not involved in the study. But she called the results "heroic and really significant."

Segal added that the research is likely to persuade more scientists to rethink the influences of genetics and environment on twins. "Twins are very alike, but it is not a perfect similarity," she said.

Words in This Story

twin – n. either of two babies who are born to the same mother at the same time

mutation – n. a change in the genes⁹ of a plant or animal

pair – n. two of the same thing

lifestyle – n. the way a person or group of people live

contribution – n. something that is add or provided to a bigger cause

implication – n. something that is suggested without being said directly

significant –adj. important

1 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。

2 genetically   

adv.遗传上

参考例句：

• All the bees in the colony are genetically related. 同一群体的蜜蜂都有亲缘关系。
• Genetically modified foods have already arrived on American dinner tables. 经基因改造加工过的食物已端上了美国人的餐桌。 来自英汉非文学 - 生命科学 - 基因与食物

3 Fertilized   

v.施肥( fertilize的过去式和过去分词 )

参考例句：

• The study of psychology has recently been widely cross-fertilized by new discoveries in genetics. 心理学研究最近从遗传学的新发现中受益匪浅。
• Flowers are often fertilized by bees as they gather nectar. 花常在蜜蜂采蜜时受粉。

4 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。

5 mutation   

n.变化，变异，转变

参考例句：

• People who have this mutation need less sleep than others.有这种突变的人需要的睡眠比其他人少。
• So far the discussion has centered entirely around mutation in the strict sense.到目前为止，严格来讲，讨论完全集中于围绕突变问题上。

6 Founder   

n.创始者，缔造者

参考例句：

• He was extolled as the founder of their Florentine school.他被称颂为佛罗伦萨画派的鼻祖。
• According to the old tradition,Romulus was the founder of Rome.按照古老的传说，罗穆卢斯是古罗马的建国者。

7 decode   

vt.译（码），解（码）

参考例句：

• All he had to do was decode it and pass it over.他需要做的就是将它破译然后转给他人。
• The secret documents were intercepted and decoded.机密文件遭截获并被破译。

8 embryo   

n.胚胎，萌芽的事物

参考例句：

• They are engaging in an embryo research.他们正在进行一项胚胎研究。
• The project was barely in embryo.该计划只是个雏形。

9 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