Question
Fri January 04, 2013 By:
 

if only a zygote has the DNA information to become a complete human,how is cloning performed?

Expert Reply
Wed January 09, 2013
Cloning an animal, or any other organism, refers to making an exact genetic copy of that organism. Two ways to do this are: artificial embryo twinning and somatic cell nuclear transfer.
 
Artificial embryo twinning is accomplished by manually separating a very early embryo into individual cells, and then allowing each cell to divide and develop on its own. The resulting embryos are placed into a surrogate mother, where they are carried to term and delivered. Again, since all the embryos came from the same zygote, they are genetically identical.
 
Somatic cell nuclear transfer (SCNT) uses a different approach than artificial embryo twinning, but it produces the same result: an exact clone, or genetic copy, of an individual.  In SCNT, the egg cell's single set of chromosomes is removed. It is replaced by the nucleus from a somatic cell, which already contains two complete sets of chromosomes. Therefore, in the resulting embryo, both sets of chromosomes come from the somatic cell.
 
The lamb Dolly  was the first-ever mammal to be cloned and it was done using this method. To make Dolly, researchers isolated a somatic cell from an adult female sheep. Next, they transferred the nucleus from that cell to an egg cell from which the nucleus had been removed. After a couple of chemical tweaks, the egg cell, with its new nucleus, was behaving just like a freshly fertilized zygote. It developed into an embryo, which was implanted into a surrogate mother and carried to term. So Dolly, was an exact genetic replica of the adult female sheep that donated the somatic cell nucleus to the egg.
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