A Clone Is a Group of Genetically Identical Organisms Or a Group of Cells Derived From

IB BIOLOGY

CLONING

A clone is a group of genetically identical organisms or a group of cells derived from a sing le parent cell.

Cloning is producing identical copies of genes, cells or organisms. The products of cloning are called a clone.

Cloning is useful if an organism has a desirable combination of characteristics and more organisms with the same characteristics are wanted- this is reproductive cloning.

Sometimes cloning is used to produce skin or other tissues needed to treat a patient – this is therapeutic cloning.

In farming, clones have been made for decades by regenerating plant material or by allowing an in-vitro fertilized egg to divide to make copies of itself.

Until recently, cloning was possible using genetic information from an egg cell. Fertilized eggs are not differentiated (specialized) yet. After dividing many times, some of the cells will specialize into muscle cells, others into nerves, others into skin and so on until a fetus is forms. For a long time, it was thought that once a cell has gone through differentiation, it cannot be used to make a clone. But then there was Dolly.

Techniques of cloning using differentiated animal cell

Reproductive cloning

Reproductive cloning creates a new individual. The best known example is Dolly the sheep. The technique used to create Dolly is known as SCNT (somatic cell nuclear transfer). The concept is simple and is illustrated in the above figure.

In 1966, a sheep by name Dolly was born. She was the first clone whose genetic material did not originate from an egg cell. This is how researchers at the Roslin Institute in Scotland produced Dolly.

· From the original donor sheep to be cloned, a somatic cell (non-gamete cell) from the udder was collected and cultured. The nucleus was removed from a cultured cell.

· An unfertilized egg was collected from another sheep and its nucleus was removed.

· Using electric current (a small and brief electric shock), the egg cell and the nucleus from the cultured somatic cell were fused together.

· The new cell developed in vitro in a similar way to a zygote and started to form an embryo.

· The embryo was placed in the womb of a surrogate mother sheep.

· The embryo developed normally.

· Dolly was born, and was presented to the world as a clone of the original donor sheep.

· Dolly is genetically identical to the sheep whose udder cells were used.

This kind of cloning is called reproductive cloning because it makes an entire individual.

It is theoretically possible to apply the same technique to cloning other species. Horses are an example of a species cloned successfully, but attempts with several other species have been less successful.

A mare and her cloned foal.

Cloning using undifferentiated cells

In some cases, scientists are not interested in making an organism but simply making copies of cells. This type of cloning is called therapeutic cloning and its aim is to develop cells which have not yet gone through the process of differentiation. Since the first technique in this area involved using embryos, the cells are referred to as embryonic stem cells, and the branch of lab work which investigates therapeutic cloning is called stem cell research.

In therapeutic cloning, human embryos are produced and allowed to grow for a few days into a small ball of cells. These cells are not yet specialized (totipotent).

Other sources of stem cells are cells from the umbilical cord or cells from aborted fetuses.

Therapeutic cloning often aims at cell therapy where diseased cells are replaced with healthy ones. Cell therapy is used for people suffering from Parkinson’s disease but may also be possible when a patient has spinal cord injury.

Bone marrow transplants for patients with leukemia, new skin cells for burn victims and to grow new corneas for some forms of visual impairments are examples of therapeutic cloning already in use.

Techniques are being developed to create human embryos, from which embryonic stem cells can be obtained for medical use. These stem cells have the capacity to divide and differentiate into any types of human cell. They could be used to replace tissues or even organs that have become damaged or lost in a patient. There are many ethical issues involved and research into therapeutic cloning has been banned in some countries.

Since therapeutic cloning starts with the production of human embryos, it raises fundamental issues of right and wrong. Is it ethically acceptable to generate a new human embryo for the sole purpose of medical research? In nature, embryos are created only for reproduction and many people believe that using them of experimentation is unnatural and wrong.

However, the use of embryonic stem cells has lead to major breakthrough in the understanding of human biology.

· Growing skin to repair serious burn;

· Growing new heart muscle to repair an ailing heart;

· Growing new kidney tissue to rebuild a failing kidney.

· With very rare exceptions, the vast majority of researchers and medical professionals are against the idea of reproductive cloning in humans. However, there is a growing popularity for the pursuit of therapeutic cloning since the promises of stem cell research are so enticing.

Arguments for therapeutic cloning

· Embryonic stem cells can be used for therapies that save lives and reduce suffering.

· The ability to cure serious diseases with cell therapy: currently leukemia and in the future possibly cancer and diabetes.

· Cells can be removed from embryos that have stopped developing, so would have died anyway.

· Cells are removed at a stage when embryos have no nerve cells and cannot feel pain.

Arguments against therapeutic cloning

· Every human embryo is a potential human being, which should be given a chance of developing.

· More embryos may be produced than are needed, so some may have to be killed.

· There is a danger of embryonic stem cells developing into tumor cells. Embryonic stem cells are capable of many divisions and may turn into tumors.

· Fears of it leading into reproductive cloning.

· Use of embryonic stem cells involves the creation and destruction of human embryos (although it is possible to use embryos left over from IVF treatment which would be destroyed anyway)