In 1997, Scottish scientists at Roslin Institute created ‘Dolly’ the cloned sheep, and she became the most renowned sheep in the world. The Science magazine acclaimed it as the “breakthrough of 1997’. However the history of cloning stretches a few decades before that. In 1952, the first animal, a tadpole, was cloned. Since Dolly, researchers have cloned a number of big and small animals including sheep, goats, cows, mice, pigs, cats, rabbits, and a gaur.
Methods of Cloning
Media coverage on cloning has stressed on only one type of cloning i.e. reproductive cloning. There are, however, different processes and types of cloning. Scientists use the term cloning to define the several technologies that lead to duplicating biological material. Also, cloning technologies can be used for purposes other than producing the genetic replica of another being. The following three types of cloning technologies are discussed here:
- Artificial Embryo Twinning
- Somatic Cell Nuclear Transfer
- Therapeutic Cloning
Artificial Embryo Cloning
This is the laboratory replication of naturally forming twins. Twins occur when a fertilized egg divides into a two-celled embryo and then the two cells separate. Each cell continues dividing on its own, and eventually forms into separate individual within the womb. As the two organisms came from the same original fertilized egg, the resulting embryos are genetically identical. Artificial embryo twinning replicates the same process outside the mother’s body. An embryo at a very early stage is manually separated into individual cells, and then each separate cell is allowed to divide and develop. The embryos thus formed are placed into a surrogate mother, where they are carried to term and delivered. As all the embryos came from the same fertilized egg or zygote, they are genetically identical.
Somatic Cell Nuclear Transfer
Though using a different technique from the above, the results are the same i.e. an exact clone, or genetic copy, of an individual. This was the method used to create Dolly the Sheep.
Every cell in the body apart from a sperm and an egg cell is termed a somatic cell. The sperm and egg cells are termed germ cells. In mammals, somatic cells have two complete sets of chromosomes and germ cells have only one complete set. The nucleus in the cell contains all the information needed to make an organism. It acts as the ‘intelligence’ of the cell’. The information is stored as the DNA and it is the DNA that makes every individual unique. Dolly was created when the nucleus from an isolated somatic cell of an adult sheep was transferred to an egg cell from which the nucleus had been removed. After being treated chemically, it developed into an embryo and was transferred into a surrogate mother. What resulted was Dolly, an exact genetic copy of the adult sheep whose cell nucleus was used.
Difference between SCNT and Natural Way of Embryo Formation
Though the end result of both the processes is the same, i.e. formation of an embryo after fertilization of an egg, there is a major difference. In natural, sexual reproduction, the embryo has the genetic material of both the egg and the sperm. In SCNT, there is a single genetic ‘parent’.
An embryo contains cells with two complete sets of chromosomes. In fertilization, the sperm and egg both contain one set of chromosomes. When the sperm and egg join, the resulting embryo gets two sets - one from the sperm and one from the egg.
In SCNT, the embryo has two sets of chromosomes, both coming from the somatic cell as the egg cell's single set of chromosomes is removed and replaced by the nucleus from a somatic cell, which already has two complete sets of chromosomes.
Therapeutic cloning, also called "embryo cloning," is the making use of human embryo in research. The objective here is to generate stem cells that can be used to study human development and to treat disease, and not to make cloned or replicas of beings. Importance of stem cells lies in the fact that they can be used to develop any type of specialized cell in the human body. Stem cells are removed from the egg after it has divided for 5 days. However, as the extraction process destroys the embryo, several ethical concerns have been raised. Scientists believe that one day stem cells can be used as replacement cells to treat heart disease, diabetes, Alzheimer's, cancer etc.
Use of Cloning Technologies
Other technologies, related to Cloning Technologies such as gene therapy, genetic engineering of organisms, and genome sequencing are important in scientific research. Gene therapy is used to treat certain genetic conditions by introducing corrected copies of faulty genes into the cell of the patient. Food crops are also engineered to improve taste and nutritional value or to increase their resistance to particular diseases. Reproductive cloning can be used to produce animals with particular features and qualities like drug producing, or those which can be modified to study human diseases.
Reintroducing endangered species and those difficult to breed can be worked out with reproductive cloning too. In 2001, the first clone of a gaur, an endangered species of wild ox. The young gaur died from an infection about 48 hours after its birth. Again, scientists in Italy cloned a healthy baby mouflon, an endangered wild sheep.
Much work is underway and may soon become a realistic option when Therapeutic cloning technology may be used in humans to produce whole organs from single cells or to produce healthy cells that can replace damaged cells in degenerative diseases such as Alzheimer's or Parkinson's.
Ethical and Moral Issues
There are groups who believe that the embryo has the moral status of a person from the moment of conception and that research or any other activity would destroy it. There are also some who believe that though the human embryo deserves respect, it would be wrong not to use embryos that would otherwise be destroyed to research potential cures for human diseases. In the USA, there are people who are against the use of federal funds for such research and find it an unethical public policy. Several groups have stated that reproductive cloning of human embryos create ethical and scientific risks. In 1997, the National Bioethics Advisory Commission recommended that it was morally unacceptable to attempt to create a child using somatic cell nuclear transfer cloning and suggested that the process be suspended until safety of this technique could be assessed. In 2001 the National Academy of Sciences stated that the US should ban human reproductive cloning because experiments with reproductive cloning in animals have proved that the process would be dangerous for the woman, the foetus, and the baby.
Risks Associated with Cloning
Though several species of mammals - sheep, cattle, pigs, goats, and mice - have been used in reproductive cloning experiments, the results have shown very limited success rates. Many of the survivors have displayed severe birth defects and many have died in the uterus itself. In addition, female animals which carry cloned foetuses ace serious risks, including death from cloning-related complications. Scientists in Tokyo have shown that cloned mice die significantly earlier than those that are naturally conceived proving that the mutations that collect in somatic cells might affect nuclear transfer efficiency and lead to diseases in the young. Dolly, the sheep, was put down by lethal injection Feb. 14, 2003 at the age of six. She had been suffering from lung cancer and crippling arthritis. Although most Finn Dorset sheep live to be 11 to 12 years of age, post-mortem examination of Dolly indicated that, other than her cancer and arthritis, she appeared to be quite normal
- The Mammel Copiers: Advances in Cloning
- Ntional Human Genome Research Institute
- Learn Genetics
- Cloning and why should we stop it
- Clonng fact sheet
- Human genome project information