2024届高考英语阅读理解五步法专项带练（41）讲义

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 (受精卵). 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 (突变) 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. ②Mutations 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, 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 may 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 of some cancers than the other. ③In 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. “It suggests 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. ④A 2008 paper in The American Journal of Human Geneticsfound some genetic differences between identical twins. The new study, however, goes beyond earlier work by including the DNA of parents