It was 10 years ago, on a warm July night, that a newborn lamb took her first breath in a small shed in Scotland. From the outside, she looked no different from thousands of other sheep born on (36)_____ farms. But Dolly, as the world soon came to realize, was no (37)_____ lamb. She was cloned from a single cell of an adult female sheep, (38)_____ long-held scientific dogma that had declared such a thing biologically impossible.
A decade later, scientists are starting to come to grips with just how different Dolly was. Dozens of animals have been cloned since that first lamb—mice, cats, cows and, most recently, a dog—and it’s becoming (39)_____ clear that they are all, in one way or another, defective.
It’s (40)_____ to think of clones as perfect carbon copies of the original. It turns out, though, that there are various degrees of genetic (41)_____. That may come as a shock to people who have paid thousands of dollars to clone a pet cat only to discover that the baby cat looks and behaves (42)_____ like their beloved pet—with a different- color coat of fur, perhaps, or a (43)_____ different attitude toward its human hosts.
And these are just the obvious differences. Not only are clones (44)_____ from the original template (模板) by time, but they are also the product of an unnatural molecular mechanism that turns out not to be very good at making (45)_____ copies. In fact, the process can embed small flaws in the genes of clones that scientists are only now discovering.
