Study: Identical Twins Are Not Genetically Exact Copies
2021-01-19
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1A new study suggests that identical twins are not exactly the same genetically.
2Identical twins are two babies that come from the same fertilized egg.
3Scientists in Iceland examined DNA from 387 pairs of identical twins, their parents, children, husbands or wives.
4The examinations led the team to find "early mutations that separate identical twins," lead researcher and geneticist Kari Stefansson said.
5He is a professor at the University of Iceland and founder of the company deCODE genetics.
6Mutations are small changes in DNA that can happen when a cell divides in an attempt to copy itself.
7These small changes can influence a person's physical appearance or control a person's ability to fight a disease.
8The newly-discovered mutations show that identical twins do have genetic differences, the researchers said.
9The results were recently published in Nature Genetics.
10On average, identical twins have 5.2 of these early genetic differences, the researchers found.
11But about 15 percent of identical twin pairs have more than that.
12Some might have as many as 100 genetic differences, Stefansson said.
13These differences represent a small part of each twin's genetic material.
14But they could influence why one twin is taller or why one is at greater risk for some cancers than the other.
15In the past, many researchers believed physical differences seen in identical twins were related mostly to environmental influences, such as nutrition or lifestyle behaviors.
16Jan Dumanski is a geneticist at Sweden's Uppsala University.
17He was not involved in the study.
18He praised the findings as "a clear and important contribution" to medical research.
19"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.
20A 2008 paper in The American Journal of Human Genetics found some genetic differences between identical twins.
21The new study, however, goes beyond earlier work by including the DNA of parents, children, husbands and wives of identical twins.
22Studying 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.
23Stefansson 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.
24However, "sometimes the second twin may show the mutation in some cells, but not all cells," he added.
25The researchers said they also found mutations that came about before the developing embryo split in two.
26Nancy Segal is a psychologist who studies twins at California State University, Fullerton.
27She was not involved in the study.
28But she called the results "heroic and really significant."
29Segal added that the research is likely to persuade more scientists to rethink the influences of genetics and environment on twins.
30"Twins are very alike, but it is not a perfect similarity," she said.
31I'm Bryan Lynn.
1A new study suggests that identical twins are not exactly the same genetically. Identical twins are two babies that come from the same fertilized egg. 2Scientists in Iceland examined DNA from 387 pairs of identical twins, their parents, children, husbands or wives. 3The 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 founder of the company deCODE genetics. 4Mutations 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. 5The newly-discovered mutations show that identical twins do have genetic differences, the researchers said. The results were recently published in Nature Genetics. 6On 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. 7These 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. 8In the past, many researchers believed physical differences seen in identical twins were related mostly to environmental influences, such as nutrition or lifestyle behaviors. 9Jan 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. 10"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. 11A 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. 12Studying 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. 13Stefansson 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. 14The researchers said they also found mutations that came about before the developing embryo split in two. 15Nancy 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." 16Segal 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. 17I'm Bryan Lynn. 18The Associated Press reported this story. Bryan Lynn adapted the report for VOA Learning English. Mario Ritter, Jr. was the editor. 19We want to hear from you. Write to us in the Comments Section, and visit our Facebook page. 20________________________________________________________________ 21Words in This Story 22twin - n. either of two babies who are born to the same mother at the same time 23mutation - n. a change in the genes of a plant or animal 24pair - n. two of the same thing 25lifestyle - n. the way a person or group of people live 26contribution - n. something that is add or provided to a bigger cause 27implication - n. something that is suggested without being said directly 28significant -adj. important