Cloning is a process of harvesting DNA from one living being and producing another living being (a molecule, a cell or an organism) which has an identical DNA makeup as that of the donor.
2. Techniques of cloning:
There are two techniques of cloning known as artificial embryo twinning and somatic cell nuclear transfer.
3. Artificial Embryo Twinning:
Artificial embryo twinning occurs on the same principle as does natural process of birth of identical twins. Fertilization occurs when a sperm penetrates an egg making a zygote, subsequently zygote undergoes serial divisions to form a fetus, however in case of identical twins the first two cells resulting from division of zygote split and go on developing into two separate individuals, the identical twins.
In case of artificial embryo twinning, similar sequence of events takes place but in a laboratory instead of mother’s womb. An early embryo is broken into individual cells and allowed to grow to be separate embryos. These embryos are then transferred into a surrogate mother and eventually delivered on maturity giving birth to a number of clones.
4. Somatic Cell Nuclear Transfer:
Somatic cell nuclear transfer is a completely different technique as compared to artificial embryo twinning. There are two types of cells in mammals somatic and germ cells. Sperms and eggs are known as germ cells or reproductive cells while all other cells in the body are known as somatic cells. Number of chromosomes in germ cells is half as compared to somatic cells so that when a sperm fertilizes an egg, the combined chromosomes of both these become equal to that of a somatic cell. In case of somatic cell nuclear transfer we remove the nucleus of an egg and then transplant a nucleus of a somatic cell into it. Now this egg becomes similar to a fertilized egg and gives rise to an embryo. This embryo is then cultured in a surrogate mother until it is mature and delivered. This offspring is, phenotypically and genotypically, exactly like the donor organism who’s DNA (nucleus) was used to fertilize the egg. The famous Dolly (the sheep) was cloned with the same technique of somatic cell nuclear transfer in 1997.
5. Human Cloning:
Human cloning is production of a genetically identical copy of a presently existing human being or of someone who existed in the past. Although natural human clones in the form of identical twins are quite common but the artificial human cloning is still in experimental phases and restricted by ethical and religious issues.