A new study suggests that identical twins are not exactly the same genetically.

一项新的研究表明，同卵双胞胎的基因并不完全相同。

Identical twins are two babies that come from the same fertilized egg.

同卵双胞胎是来自同一个受精卵的两个婴儿。

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

冰岛科学家检测了387对同卵双胞胎、还有他们的父母、孩子、丈夫或妻子的DNA。

The examinations led the team to find "early mutations that separate identical twins,"

研究小组发现了“区分同卵双胞胎的早期突变”，

lead researcher and geneticist Kari Stefansson said.

首席研究员、遗传学家凯里·斯蒂芬森说。

He is a professor at the University of Iceland and founder of the company deCODE genetics.

他是冰岛大学的教授，也是deCODE遗传学公司的创始人。

Mutations are small changes in DNA that can happen when a cell divides in an attempt to copy itself.

突变是DNA中的微小变化，当细胞分裂试图复制自身时可能发生。

These small changes can influence a person's physical appearance or control a person's ability to fight a disease.

这些微小的变化会影响一个人的外表或控制一个人对抗疾病的能力。

The newly-discovered mutations show that identical twins do have genetic differences, the researchers said.

研究人员说，新发现的突变表明同卵双胞胎确实存在基因差异。

The results were recently published in Nature Genetics.

该研究结果最近发表在《自然遗传学》杂志上。

On average, identical twins have 5.2 of these early genetic differences, the researchers found.

研究人员发现，每对同卵双胞胎平均有5.2个早期基因差异。

But about 15 percent of identical twin pairs have more than that.

但是，大约15%的同卵双生子基因差异更多。

Some might have as many as 100 genetic differences, Stefansson said.

斯蒂芬森说，有些可能有多达100个基因差异。

These differences represent a small part of each twin's genetic material.

这些差异只是每对双胞胎遗传物质的一小部分。

But they could influence why one twin is taller or why one is at greater risk for some cancers than the other.

但它们可能会影响双胞胎中为什么一个比另一个高，或者为什么一个比另一个患某些癌症的风险更大。

In the past, many researchers believed physical differences seen in identical twins were related mostly to environmental influences,

过去，许多研究人员认为，同卵双胞胎的身体差异主要与环境影响有关，

such as nutrition or lifestyle behaviors.

如营养或生活方式。

Jan Dumanski is a geneticist at Sweden's Uppsala University.

扬·杜曼斯基是瑞典乌普萨拉大学的遗传学家。

He was not involved in the study.

他没有参与这项研究。

He praised the findings as "a clear and important contribution" to medical research.

但他称赞这些发现为医学研究做出了“明确而重要的贡献”。

"The implication is that we have to be very careful when we are using twins as a model"

“这意味着，我们必须非常小心。”

for examining the influences of genetics or the environment, Dumanski said.

当我们用双胞胎作为研究基因或环境影响的模型时，杜曼斯基说。

A 2008 paper in The American Journal of Human Genetics found some genetic differences between identical twins.

2008年发表在《美国人类遗传学杂志》上的一篇论文发现，同卵双胞胎之间存在一些基因差异。

The new study, however, goes beyond earlier work

然而，这项新的研究超越了当时的工作，

by including the DNA of parents, children, husbands and wives of identical twins.

包括了同卵双胞胎的父母、孩子、丈夫和妻子的DNA。

Studying family members permitted the researchers to examine when genetic mutations happened in two different kinds of cells:

通过研究家庭成员，研究人员可以检查两种不同类型的细胞何时发生了基因突变:

those present in only one individual and those passed on to the person's children.

一种是只存在于一个人身上的，另一种是遗传给孩子的。

Stefansson said his team found twins where a mutation is present in all cells of the body of one twin, but not in the other twin at all.

斯蒂芬森说，他的团队发现了一对双胞胎，其中一个的所有细胞都有突变，而另一个完全没有。

However, "sometimes the second twin may show the mutation in some cells, but not all cells," he added.

然而，“有时第二个双胞胎可能在某些细胞中显示出突变，但不是所有细胞，”他补充说。

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

研究人员说，他们还发现在发育中的胚胎分裂为两部分之前就出现了突变。

Nancy Segal is a psychologist who studies twins at California State University, Fullerton.

南希·西格尔是一名心理学家，在富勒顿的加州州立大学研究双胞胎。

She was not involved in the study.

她没有参与这项研究。

But she called the results "heroic and really significant."

但她称这些结果“英勇且意义重大”。

Segal added that

西格尔补充说，

the research is likely to persuade more scientists to rethink the influences of genetics and environment on twins.

这项研究可能会说服更多的科学家重新思考基因和环境对双胞胎的影响。

"Twins are very alike, but it is not a perfect similarity," she said.

她说:“双胞胎非常相似，但也不是完全相似。”

I'm Bryan Lynn.

布莱恩·林恩报道。

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