What is cloning? Are there different typ

题目：

What is cloning? Are there different types of cloning?

_____71____ Actually, there are different technologies which can be used for other purpose besides producing the genetic twin of another organism. A basic understanding of the different types of cloning is key to talking an informed stance on current public policy issues and making the best possible personal decisions. The following three types of cloning technologies are usually performed; recombinant DNA technology or DNA cloning, reproductive cloning, and therapeutic cloning.

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Scientists have been cloning animals for many years. In 1952, the first animal, a tadpole, was cloned. ___73_____ Since Dolly, researchers have cloned a number of large and small animals including sheep, goats, cows, mice, pigs, cats, rabbits, and a gaur. ____74____

Hundreds of cloned animals exist today, but the number of different species is limited. ____75____ Some species may be more resistant to somatic cell nuclear transfer than others. The process of stripping the nucleus from an egg cell and replacing it with the nucleus of a donor cell is a traumatic one, and improvements in cloning technologies may be needed before many species can be cloned successfully.

A．What animals have been cloned?

B．All these clones were created using nuclear transfer technology

C．When the media report on cloning in the news, they are usually talking about only one type called reproductive cloning.

D．Recently Chinese scientists have also successfully cloned mammals such as an ox.E.       Cloning is making a genetic copy of something else.

F.       Attempts at cloning certain species such as monkeys, chickens, horses, and dogs, have been unsuccessful.

G.       Before the creation of Dolly, the first mammal cloned from the cell of an adult animal, clones were created from embryonic cells.