What is Cloning?

What is Cloning?


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.

Twin girls

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.

1. Artificial Embryo Twinning




2. Somatic Cell Nuclear Transfer


What does SCNT mean? Let's take it apart:



Transfer: Moving an object from one place to another. To make Dolly, researchers isolated a somatic cell from an adult female sheep. Next they removed the nucleus and all of its DNA from an egg cell. Then they transferred the nucleus from the somatic cell to the egg cell. After a couple of chemical tweaks, the egg cell, with its new nucleus, was behaving just like a freshly fertilized egg. It developed into an embryo, which was implanted into a surrogate mother and carried to term. (The transfer step is most often done using an electrical current to fuse the membranes of the egg and the somatic cell.)

The lamb, Dolly, was an exact genetic replica of the adult female sheep that donated the somatic cell. She was the first-ever mammal to be cloned from an adult somatic cell.

Watch these videos of enucleation and nuclear transfer.


Natural fertilization, where egg and sperm join, and SCNT both make the same thing: a dividing ball of cells, called an embryo. So what exactly is the difference between the two?

An embryo's cells all have two complete sets of chromosomes. The difference between fertilization and SCNT lies in where those two sets come from.

In fertilization, the sperm and egg have one set of chromosomes each. When the sperm and egg join, they grow into an embryo with two sets—one from the father's sperm and one from the mother's egg.

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. So, in the resulting embryo, both sets of chromosomes come from the somatic cell.

Is cloning an organism the same as cloning a gene?


When scientists clone an organism, they are making an exact genetic copy of the whole organism, as described above.


cloning a gene

Supported by a Science Education Partnership Award (SEPA) Grant No. R25RR016291 from the National Center for Research Resources, a component of the NIH. The contents provided here are solely the responsibility of the authors and do not necessarily represent the official views of NIH.


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APA format:
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