B
A new study suggests that identical(同卵的) twins are not exactly the same genetically. Scientists in Iceland examined DNA 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.
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 genetic differences. On average, identical twins have 5.2 of these early genetic differences, the researchers found. 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 mutation 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.
44．What is a function of mutations?
A．Change people’s DNA．
B．Help a cell to copy itself.
C．Influence people’s physical appearance.
D．Increase people’s ability to fight diseases.
45．Why did the study include the DNA of family members?
A．To check when the mutations happened.
B．To identify the results of former research.
C．To find out where the mutations happened.
D．To examine the influence of the environment.
46．What is Jan Dumanski’s attitude toward the study?
A．Cautious. B．Doubtful.
C．Concerned. D．Positive.
47．Which of the following is the best title for the text?
A．A Breakthrough in Identical Twins Study
B．Identical Twins: Not Genetically Exact Copies
C．Genetic Differences Caused by Family Members
D．DNA Decides the Difference between Identical Twins
【分析】
这是一篇说明文。文章介绍了一项新的研究表明同卵双胞胎在基因上并不完全一样。
44．
细节理解题。根据第二段“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.”（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。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）可知，突变的作用是影响人的外貌。故选C项。
45．
细节理解题。根据第六段中“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.”（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：一种是只存在于一个人身上的，另一种是遗传给孩子的）可知，研究家庭成员可以查明突变在何时发生。故选A项。
46．
推理判断题。根据第五段中“He praised the findings as ‘a clear and important contribution’ to medical research.”（他称赞这些发现为医学研究做出了“明确而重要的贡献”）可以推知，Jan Dumanski对研究结果大加赞赏，也就是持积极的态度，故选D项。
47．
主旨大意题。通读全文，特别是根据第一段“A new study suggests that identical(同卵的) 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）可知，本文主要介绍一项新的研究，表明同卵双胞胎的基因并不完全相同。选项B“同卵双胞胎：基因上不是完全相同的复制品”高度概括文章主题，准确全面，适合作标题。故选B项。
A new study suggests that identical(同卵的) twins are not exactly the same genetically. Scientists in Iceland examined DNA 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.
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 genetic differences. On average, identical twins have 5.2 of these early genetic differences, the researchers found. 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 mutation 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.
44．What is a function of mutations?
A．Change people’s DNA．
B．Help a cell to copy itself.
C．Influence people’s physical appearance.
D．Increase people’s ability to fight diseases.
45．Why did the study include the DNA of family members?
A．To check when the mutations happened.
B．To identify the results of former research.
C．To find out where the mutations happened.
D．To examine the influence of the environment.
46．What is Jan Dumanski’s attitude toward the study?
A．Cautious. B．Doubtful.
C．Concerned. D．Positive.
47．Which of the following is the best title for the text?
A．A Breakthrough in Identical Twins Study
B．Identical Twins: Not Genetically Exact Copies
C．Genetic Differences Caused by Family Members
D．DNA Decides the Difference between Identical Twins
【分析】
这是一篇说明文。文章介绍了一项新的研究表明同卵双胞胎在基因上并不完全一样。
44．
细节理解题。根据第二段“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.”（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。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）可知，突变的作用是影响人的外貌。故选C项。
45．
细节理解题。根据第六段中“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.”（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：一种是只存在于一个人身上的，另一种是遗传给孩子的）可知，研究家庭成员可以查明突变在何时发生。故选A项。
46．
推理判断题。根据第五段中“He praised the findings as ‘a clear and important contribution’ to medical research.”（他称赞这些发现为医学研究做出了“明确而重要的贡献”）可以推知，Jan Dumanski对研究结果大加赞赏，也就是持积极的态度，故选D项。
47．
主旨大意题。通读全文，特别是根据第一段“A new study suggests that identical(同卵的) 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）可知，本文主要介绍一项新的研究，表明同卵双胞胎的基因并不完全相同。选项B“同卵双胞胎：基因上不是完全相同的复制品”高度概括文章主题，准确全面，适合作标题。故选B项。
