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Is it possible for a child to have three parents? A paper just published in Nature by Shoukhrat Mital-ipov and his colleagues se

admin2014-06-25  56
问题     Is it possible for a child to have three parents? A paper just published in Nature by Shoukhrat Mital-ipov and his colleagues seems answer "yes", for this study paves the way for the birth of children who, genetically, have one father, but two mothers.
    The reason this is possible is that a mother’s genetic contribution to her offspring comes in two separable pieces. By far the largest is packed into the 23 chromosomes in the nucleus of an unfertilized egg. Besides, the mother also contributes what is known as mitochondrial DNA. And it is that fact which has allowed doctors to conceive of the idea of people with two mothers; one providing the nuclear DNA and one the mitochondrial sort. The reason for doing this is that mutations in mitochondrial DNA can cause disease. Each particular mitochondrial disease is rare. But there are lots of them. Mitochondrial disease is thus not a huge problem, but it is not negligible, either.
    However, turning the experiment of mitochondrial transplantation into a medical procedure would be a long road, and not just scientifically. Dr Mitalipov has little doubt that his zygotes could be brought to term if they were transplanted into a woman’s womb. That experiment, though, is illegal. But the fact that it now looks possible will surely stimulate debate about whether the law should be changed.
    Two kinds of questions arise. One kind is practical: would the process usually work and, if it did, would it always lead to a healthy baby who would have a normal chance of growing into a healthy adult? The second kind of question is moral, for what is being proposed is, in essence, genetic engineering. Not, perhaps, as classically conceived because no DNA is artificially modified. But it is engineering nevertheless, which might worry some people.
    On the first kind of question, the signs are good. When Dr Mitalipov tested his zygotes, he could find no trace of mutated mitochondrial DNA. It is on the moral questions that things may stumble. Some people oppose such genetic modification in principle. Some worry about the consequences of a third adult being involved in the traditionally two-person process of parenthood though the mitochondrial contribution is restricted to genes for energy-processing proteins and is unlikely to have wider influences on family resemblance. Some worry that three-parented individuals may themselves be worried by knowledge of their origin.
    In the end, whether three-parent children are permitted will probably depend on the public "uggh!" factor. There was once opposition to in vitro fertilisation, with scornful terms like "test-tube baby" being spread about. Now, IVF is routine, and it is routine because it is successful. What will probably happen to mitochondrial transplants is that one country permits the procedure, and the world will then see the consequences. If they are good, you will never find anyone who will admit to having opposed the transplants in the first place. If they are bad, the phrase "I told you so" will ring aloud.
The application of mitochondrial transplantation might occur when______.
选项 A、medical technology becomes highly developed
B、it can be tested to lead to a healthy baby
C、it is proven that family resemblance will not be affected
D、genetic engineering is socially accepted
答案D
解析 文中第四段指出，线粒体移植面I临两类问题：第一类是实际性的，第二类是道德上的。第五段进一步指出，第一类问题前景比较乐观，而第二类问题才是真正棘手的，因为人们对基因工程的不接受及各种担忧。据此可推出，公众的接受与否是决定线粒体移植实际应用的主导因素，而第六段“最终是否会出现三位父母很可能取决于公众的马后炮行为”进一步印证了这一推测，[D]选项正确。
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