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  3. When a Massachusetts biotech company recently declared that its researchers h

When a Massachusetts biotech company recently declared that its researchers h

游客2023-12-17  48
问题    When a Massachusetts biotech company recently declared that its researchers had cloned human embryos, it conjured up scary images for many people: bad science-fiction movies, Hitler’s twisted ambitions, rows and rows of identical humans.
   But, like most things in life, the truth is a lot more complicated, more subtle.
   The announcement drew a storm of criticism.  Ethicists, religious leaders and US President Bush denounced Advanced Cell Technology for going too far. Scientists charged that the experiment was hyped and called it a failure.
   The news put a spotlight on the field of cloning, from work with animals to researchers’ efforts to use cloning to create tissues for people suffering from debilitating and fatal diseases.
   At its most basic level, cloning means creating copies, and in many ways, cloning has been around a long time. When someone cuts a shoot off a green spider plant and re-pots it, that person is creating a clone. Scientists clone or copy genetic material, or DNA, to match suspects to crimes. By copying cells, researchers have been able to create and test drugs. Scientists even use cloning techniques to create copies of the human gene for insulin to help make insulin for people with diabetes.
   "Cloning per se is not bad.  The ability to clone and make lots of copies of DNA molecules and cells is part of the entire biological revolution and all sorts of good stuff," sags Larry Goldstein, professor of cellular medicine at the University of California, San Diego, School of Medicine.
   Cloning a whole animal or a human being, however, is a much more difficult proposition, even without considering the moral implications.  The basic method sounds deceptively simple. Scientists allow an egg to mature in a culture dish.  They strip out the genetic material from this egg. Then they insert the genetic material of a separate cell, an adult cell. Next, using a chemical mixture or electrical stimulation, researchers trick the egg into thinking it has been fertilised by sperm. This will activate the cell to start dividing.
   Essentially, scientists are trying to reprogramme the egg to create a new organism. It’s an excruciatingly difficult process.  During the past several years, scientists around the world have used this method to clone animals. They’ve created about a half-dozen different species, including the famous first sheep, Dolly, along with cows, mice, goats and pigs. Experts say these cloned animals could offer a great deal, from herds that produce more milk, to genetically modified animal organs that could be used for transplantation in humans, and even to cattle that lack the gene that makes them susceptible to mad cow disease.
    But it has been a tough process. For each species, scientists have had to work out subtle variations on the basic cloning steps, including how to treat the donor cell and what type of stimulation to use to spark the egg to start dividing. Still, fewer than 1% of these cloned embryos produce live offspring.
   Even those born alive have abnormalities--some become obese very quickly, some suffer neonatal respiratory failure. Those that die do so suddenly, and scientists can’t figure out why.
   There is no consensus about what is going wrong in these experiments or why, except that something must be awry in the genetic reprogramming. But almost all scientists agree that aside from the moral debate, cloning hasn’t been perfected enough to try in humans. [br] In the process of cloning, what ultimately activates the cell to start dividing?
选项 A、An adult cell inserted into an egg.
B、An electronic stimulation.
C、An artificially fertilised egg.
D、Another donor cell.
答案 C
解析 第七段描述了克隆的过程。首先，科学家们从成熟的卵子里剥离出所需的基因。然后在该基因中注入一个成人的细胞。接着，用化学药剂或是电击刺激该卵子，使它误以为被受精。最后，被受精的卵子激活被注入的细胞并使其分裂。由此可见，最终使细胞分裂的是人工受精卵。因此选C。
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