[NatashaKundi]

What is Cloning?
It is a process by which an identical copy of DNA is produced. It is used to reproduce type specific cells such as an individual organism like Dolly Sheep. Unlike normal reproduction, cloning requires a single parent. A few types of plants have been cloned in the course of many years but cloning of animals especially humans is an ethical issue. Cloning enables illnesses to be cured and to make plants healthier.

Cloning is done by using a circular DNA as a carrier in which a foreign piece of DNA is put. Special genetic information is held within this foreign piece of DNA. The circular DNA is called a vector which acts as a means of transport. The vector then replicates and is then transferred from one living organism to another. This living organism is called a host as its body acts as a temporary home for this DNA and its vector. The new circular DNA with the foreign piece is called a clone which is different from the parental vector.

Nuclear Transfer is a type of cloning that involves transfer of nucleus from a somatic cell (e.g. blood cell, heart cell) to an egg cell. The nucleus of the somatic cell is removed by a micropipette and injected into an enucleated oocyte, which is an unfertilized cell. The nucleus is then given an electric shock so as to fuse with the cytoplasm. It then divides until it becomes an embryo and is then implanted into a surrogate thus giving rise to an identical organism.

Artificial Twinning is also a type of cloning in which an embryo is artificially divided into two or more embryos. An egg is fertilized by sperm. In the early stages of its formation, the embryo is split into two or more embryos which are then left to grow in a surrogate. The offspring thus produced are identical.

Before the birth of Dolly Sheep, an experiment was performed on frog cells. Nucleus from a frog’s gut cell was injected into an enucleated oocyte. The cell began to divide until an embryo was formed thus resulting in tadpoles. Earlier on, this technique only worked on frogs. Scientists could not clone mammals. Another drawback was that the tadpoles never grew into frogs; they died at a very early stage.

After a lot of experimentation, scientists discovered that using a quiescent (undividable) cell instead of a fast dividing cell will prove helpful in cloning of mammals. Therefore they started an experiment on sheep. The method used was Nuclear Transfer. They took a cell from the mammary glands of a Finn Dorset breed of sheep, removed the nucleus and injected it into a Blackface ewe breed. An electric pulse was then used to fuse the nucleus with the cytoplasm of the cell. This fused cell was then transferred into a Blackface ewe. This process was repeated 276 times and after 148 days, Dolly Sheep was born on 5th July 1996. This success enabled scientists to clone domestic animals such as cows, horses, bulls etc. After being bred with a Welsh Mountain ram, Dolly gave birth to six lambs. She then died at the age of six as she developed lung diseases and arthritis.