2. 外语
  3. Dolly the clone (克隆羊多利) was born a lamb, but her chromosomes (染色体) tell a differen story. They say she was already a few years o

Dolly the clone (克隆羊多利) was born a lamb, but her chromosomes (染色体) tell a differen story. They say she was already a few years o

admin2012-07-18  71
问题     Dolly the clone (克隆羊多利) was born a lamb, but her chromosomes (染色体) tell a differen story. They say she was already a few years old by the time she left her mother’s womb.
    Scientists at the Roslin Institute in Scotland finally took a close look at Dolly’s chromosomes and found that their ends, or telomeres(端粒—染色体端位上的着色点)， are shorter than those of normal sheep of Dolly’s age. Telomeres, scientists think, are a major factor in aging—the shorter they are, the closer the cell is to dying.
    The scientists also looked at the telomere length of two other sheep, one cloned from a 9-day-old embryonic cell(受孕的胚胎细胞) and the other from a 25-day -old fetal cell. The sheep cloned from the 9-day -old cell had the longest telomeres of the three, suggesting that the key factor in determining telomere length seems to be the number of divisions the cell undergoes before being cloned.
    All three clones appear to be healthy, and whether the animals will have a shorter life span as a result of their shorter telomeres remains an open question. But the shortened telomeres do suggest that genetic blueprints may wear out over time, making it impossible to clone an animal endlessly.
Among the three mentioned the sheep cloned from a 1-day old embryonic cell is the youngest.
选项 A、Right.
B、Wrong.
C、Doesn’t say.
答案A
解析 见第三段最后一句。
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