A look at the different types of cloning and their uses.
When you read about cloning in the news, they are usually talking about reproductive cloning, however this is only one type of cloning, there is also DNA cloning and therapeutic cloning.
DNA cloning
DNA cloning, also known as recombinant DNA technology, occurs when a piece of DNA from one organism is transferred to a self replicating genetic element such as a bacterial plasmid. The plasmid is then transferred to a bacterium, where multiple copies of the same gene are generated. DNA cloning is used by scientists to copy genes and to create enough material for further study.
Reproductive cloning
Reproductive cloning is used to create an animal that has the same DNA as another animal. The famous Dolly the sheep was the first animal created by reproductive cloning. The scientists, using a technique called somatic cell nuclear transfer, transfer genetic material taken from an adult cell nucleus to an egg whose nucleus has been removed. The egg, now containing the adult donor genetic material is then treated with chemicals or an electric current to trigger cell division. When the cloned embryo reaches a certain stage, it is transplanted to the uterus of a female of the same species where the pregnancy continues hopefully as normal.
Dolly and other animals created using nuclear transfer technology are not true identical clones. Only the clone’s chromosomal DNA is the same as the donor's DNA. There is also genetic material in the mitochondria, which reside in the cytoplasm of the egg cell that had its nucleus removed. The mitochondrial DNA is also replicated as the cell divides and this mitochondrial DNA will be from the animal that donated the egg cell and not from the donor animal.
Dolly proved that the genetic material from a specialized adult cell, such as an udder cell, which is programmed to express only udder cell genes, could be reprogrammed to create an entirely new creature. Prior to Dolly, scientists believed that once a cell had become specialized as a certain type of cell, the change was permanent. Some scientists believe that errors in reprogramming during reproductive cloning leads to the high numbers of dead or deformed animal clones.
Since Dolly the sheep, scientists have cloned animals such as goats, cows, mice, pigs and cats. However, attempts at cloning monkeys, chickens, horses and dogs have been unsuccessful.
If the low success rate or reproductive cloning can be improved, it could be used as an efficient method of reproducing animals with special qualities. It could also be used to repopulate endangered animals.
Therapeutic Cloning
Therapeutic cloning, also known as embryo cloning, is the production of human embryos for research purposes. They are used to harvest stem cells that are used in human development research and potentially in the treatment of many diseases. Stem cells can be used to generate virtually any type of specialized cell in the human body. Stem cells are extracted from the embryo when it is 5 days old, the extraction process destroys the embryo and this raises ethical concerns. Many scientists hope that one day stem cells can be used as replacement cells to treat diseases like heart disease and Alzheimer’s. It may even be used to generate tissues and organs for transplant, significantly reducing the need for organ donation.
To read about cloning's place within the wider realm of biotechnology, click here.
Sources:
Cloning fact sheet – Human Genome Project Information
