Types de clonage

Cloning is a scientific term signifying numerous processes that can be used to create genetically identical copies of a biological entity including cells, tissues and entire organisms. It exists under various artificial forms such as gene cloning, reproductive cloning and therapeutic cloning. However, this biological discovery is also present naturally when single-celled organisms such as bacteria produce genetically identical offspring through a process called asexual reproduction. Moreover, it is witnessed as identical twins occur in humans and other mammals. They are obtained when a fertilized egg splits, creating two or more embryos that carry almost identical DNA.

1. Types of cloning

a) Gene cloning

As previously mentioned, artificial cloning appears through 3 different types. Firstly, gene cloning: a process that involves the production of copies of genes or segments of DNA. It is the most commonly practiced cloning by researchers at the National Human Genome Research Institute for educational matters. It is made by implanting a gene from an organism into a vector -bacteria, yeast cells, viruses or plasmids, which are small DNA circles carried by bacteria- that leads to its multiplication as many times over.

b) Reproductive cloning

Secondly, reproductive cloning which is a procedure that creates copies of whole organisms such as animals whom have been actually cloned before. It consists the removal of a somatic cell- any cell in the body other than sperm and egg, the two types of reproductive cells- such as the skin cell from an organism that is wanted to be cloned. Then, they transfer its DNA into an egg cell that has its nucleus- a compartment that holds the cell's DNA- removed. The egg afterwards is meant to develop into an early-stage embryo in the test-tube and then is implanted into the womb of an adult female animal. One of the famous cloned animals is the experiment of Dolly the sheep that has been the first success in 1997 and the most well-known case in the field.

i) What animals have been cloned?

Throughout the past five decades, cloning has been developing and growing with its scientific applications and experiments. Despite the fact that human cloning is still considered as fiction and that it has never been truly proven, animal cloning has been more commonly studied each day. Starting from 1979, researchers were able to produce the first genetically identical mice under the theory of artificial embryo twinning. This trial has been applied by separating a very early embryo into individual cells. Each half of the embryo continues to divide on its own forming two whole organisms. Reaching this point, they are implanted into a surrogate mother or in this case, into the wombs of adult female mice. Furthermore, under the name of productive cloning, researchers produced the first genetically identical cows, sheep and chickens. However, it was only in 1996 and after 276 attempts, Scottish researchers have succeeded in cloning the first mammal from a mature cell taken from an adult animal by producing Dolly, the lamb. Moreover, in 1998, the Japanese were able to clone eight calves from a single cow. Lately, for educational matters, various animals have also been cloned such as: cat, deer, dog, horse, mule, ox, rabbit and rat.

ii) Are cloned animals physically identical to their donor?

Even though they do share the exact same genetic material, cloned animals do not always look identical. As a matter of fact, the environment is one of the aspects that influence severely an organism and helps determinate its appearance. This has been shown by the example of CC the cat that looked very different from her mother as the color and patterns of the cat aren’t exclusively a result to its gene formation but also in the distribution of its chromosomes.

iii) The benefits of reproductive cloning

Reproductive cloning, especially animal cloning has been and could be very beneficial through the past and upcoming years. It has many advantages considering the fields of medicine and agriculture. For example, Scottish researches have also cloned sheep that are meant to produce milk that contains a human protein necessary for blood clotting. It has for aim to be later purified from the milk and given to humans with problems in blood clotting.

...