译林2003课标版《Reading(1)： The perfect copy》公开课PPT课件优质课下载

译林2003课标版《Reading(1)： The perfect copy》公开课PPT课件优质课下载

Clones are organisms that are exact genetic copies. Every single bit of their DNA is identical.

Clones can happen naturally—identical twins are just one of many examples. Or they can be made in the lab. Below, find out how natural identical twins are similar to and different from clones made through modern cloning technologies.

How Is Cloning Done?

Many people first heard of cloning when Dolly the Sheep showed up on the scene in 1997. Artificial cloning technologies have been around for much longer than Dolly, though.

There are two ways to make an exact genetic copy of an organism in a lab: artificial embryo twinning and somatic cell nuclear transfer.

A dog or a eagle?

A frog or a crocodile?

A tortoise or a bear?

A dog or a man?

Do you think they are perfect cloned animals?

2. Somatic Cell Nuclear Transfer

Somatic cell nuclear transfer (SCNT), also called nuclear transfer, uses a different approach than artificial embryo twinning, but it produces the same result: an exact genetic copy, or clone, of an individual. This was the method used to create Dolly the Sheep.

Title understanding

How can you understand the word copy?

A. model

B. clone

C. similarity

D. imitation

cloned pigs

scientific term

（科学术语）

1. Artificial Embryo Twinning

Artificial embryo twinning is a relatively low-tech way to make clones. As the name suggests, this technique mimics the natural process that creates identical twins.

In nature, twins form very early in development when the embryo splits in two. Twinning happens in the first days after egg and sperm join, while the embryo is made of just a small number of unspecialized cells. Each half of the embryo continues dividing on its own, ultimately developing into separate, complete individuals. Since they developed from the same fertilized egg, the resulting individuals are genetically identical.

Is cloning an organism the same as cloning a gene?