Clone and Cloning

The cloning of specific genes can provide large numbers of copies of the gene for use in genetics, medical research, and systematics. Gene cloning begins by separating a specific length of DNA that contains the target gene. This fragment is then placed into another DNA molecule called the vector, which is then called a recombinant DNA molecule. The recombinant DNA molecule is used to transport the gene into a host cell, such as a bacterium or yeast, where the vector DNA replicates independently of the nuclear DNA to produce many copies, or clones, of the target gene. Recombinant DNA can also be introduced into plant or animal cells, but if the cells are to produce a particular protein (e.g., hormone or enzyme) for a long time, the introduced DNA molecule has to integrate into the nuclear DNA.

In nature, the simple organisms such as bacteria, yeast, and some other small organisms use cloning (asexual reproduction) to multiply, mainly by budding.

The cloning of animal cells in laboratories has been achieved through two main methods, twinning and nuclear transfer. Twinning occurs when an early stage embryo is divided in vitro and inserted into surrogate mothers to develop to term. Nuclear transfer relies on the transfer of the nucleus into a fertilised egg from which the nucleus was removed. The progeny from the first procedure is identical to each other while being different from their parents. In contrast progeny from the second procedure share only the nuclear DNA with the donor, but not mitochondrial DNA and in fact it is not identical to the donor.

In 1993, the first human embryos were cloned using a technique that placed individual embryonic cells (blastomeres) in a nutrient culture where the cells then divided into 48 new embryos. These experiments were conducted as part of some studies on in vitro (out of the body) fertilization aimed at developing fertilized eggs in test tubes, which could then be implanted into the wombs of women having difficulty becoming pregnant. However, these fertilized eggs did not develop to a stage that was suitable for transplantation into a human uterus.

Cloning cells intially held promise to produce many benefits in farming, medicine, and basic research. In agriculture, the goal is to clone plants containing specific traits that make them superior to naturally occurring plants. For example, in 1985, field tests were conducted using clones of plants whose genes had been altered in the laboratory (by genetic engineering) to produce resistance to insects, viruses, and bacteria. New strains of plants resulting from the cloning of specific traits could also lead to fruits and vegetables with improved nutritional qualities and longer shelf lives, or new strains of plants that can grow in poor soil or even under water. A cloning technique known as twinning could induce livestock to give birth to twins or even triplets, thus reducing the amount of feed needed to produce meat.

In medicine, gene cloning has been used to produce vaccines and hormones, for example: insulin for treating diabetes and of growth hormones for children who do not produce enough hormones for normal growth. The use of monoclonal antibodies in disease treatment and research involves combining two different kinds of cells (such as mouse and human cancer cells), to produce large quantities of specific antibodies, which are produced by the immune system to fight off disease.