普通高中课程标准实验教科书 英语选修8 Unit 2 Cloning-Using La

The possibility of cloning fierce and extinct wild animals has always excited film makers¹. And they are not the only ones! The popularity of films such as Jurassic Park, in which a scientist clones several kinds of extinct dinosaurs², proves how the idea struck a mixture of fear and excitement into people's hearts. But in fact we are a long way from being able to clone extinct animals. Scientists are still experimenting with cloning mammals. This is because the cloning of mammals is still a new science and its story only began seriously in the 1950s as this list shows:
 
   1950s cloning of frogs                                                1996 first clone of a mammal: Dolly the sheep
   1970s research using the embryos³ of mice             2000 cow gave birth to a bison
   1979 work on embryos of sheep and mice              2001 China's first cloned twin calves
   1981 first experimental clones of mice                     2002 first cloned cats
   1983 first experimental clones of cows                     2005 first cloned dog
                                                                                            …
 
         From time to time people suggest that extinct animals like dinosaurs, can possibly be brought back to life through cloning. Unfortunately, with what we know now, this is either impossible or unsuitable. There are many reasons.
◎ The initial requirement is that you need perfect DNA⁴ (which gives information for how cells
     are to grow).
◎ All efforts of cloning an animal will be in vain if there is not enough diversity in the group to overcome illnesses. Diversity in a group means
     having animals with their genes⁵ arranged in different ways. The advantage is that if there is a new illness some of these animals may die,
     but others will survive and pass on the ability to resist that disease to the next generation. The great drawback to cloning a group of
     animals is that they would all have the same arrangement of genes and so might die of the same illness. Then none of them would be left to
     continue the species.
◎ It would be unfair to clone any extinct animals if they were to live in a zoo. A suitable habitat would be needed for them to lead a natural life.
 
         Based on what we know now, you cannot clone animals that have been extinct longer than 10,000 years. Actually, dinosaurs disappeared 65,000,000 years ago. So the chance of dinosaurs ever returning to the earth is merely a dream.

1 makers   

n.制造者，制造商（maker的复数形式）

参考例句：

• The makers of the product assured us that there had been no sacrifice of quality. 这一产品的制造商向我们保证说他们没有牺牲质量。
• The makers are about to launch out a new product. 制造商们马上要生产一种新产品。 来自《简明英汉词典》

2 dinosaurs   

n.恐龙( dinosaur的名词复数 )；守旧落伍的人，过时落后的东西

参考例句：

• The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
• Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》

3 embryos   

n.晶胚；胚，胚胎( embryo的名词复数 )

参考例句：

• Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段，而且其行为象胚。 来自辞典例句
• Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句

4 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

5 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪