3.3. Cloning

Unit 4: The genetic revolution 1 2 3 4

3.3. Cloning

Cloning is the process by which an identical genetic copy (clone) of a cell or organism is obtained.

Plants and some animals such as sponges can reproduce asexually. They maintain during all their adult lives, totipotent undifferentiated cells equivalent to embryonic stem cells. In these cases cloning is a natural process, as it also occurs in human twins. However, since some decades it is possible to obtain in laboratory, clones from differentiated cells. This is the sense in which the term “cloning” is used today.

a) Reproductive cloning

In 1996, in the Roslin Institute of Edimburg (Scotland) a clone from the cells of an adult animal was obtained for the first time. As a result, the sheep Dolly was born, the first clone mammal of the history. Since then, other mammals has been cloned (sheep, pigs, goats, mice, cats and primates).

The technique used is called nuclear transfer. The procedure is the following:

1st) Obtaining of a somatic cell from the individual we want to clone

(mammary gland cell)

2nd) Extraction of an ovum of a donor female.

3rd) Elimination of the nucleus of the ovum.

4th) Transfer of the adult cell to the ovum without nucleus.

5th) The obtained cell (an artificial zygote) is cultured in laboratory.

6th) When this embryo reach the morula stage is implanted in the uterus of another

different female (surrogate mother).

7th) After the period of gestation a new individual in born.

This individual is a clone of the individual that donor the adult cell.

Although cloning can seem a simple and controlled process, it is not. Nowadays, cloning in animals is very expensive, little efficient and not always is successful. For Dolly get to born, 400 ova were necessary and only 277 could be fussed with the somatic cell. After the first divisions of the zygote only 50 embryos were viable and transferred to surrogate mothers. Only 13 females got pregnant and only one could have a living young, Dolly.

Possible applications of reproductive cloning are related to:

Obtaining of animals and plants of economic, nutritional or investigation interest

Recuperation of endangered or extinct species.

Obtaining of organs for transplants (xenotransplants)

b) Therapeutic cloning

The goal in this case is the obtaining of pluripotent cells from adult cells of a patient to use them in self-transplants to avoid the risk of rejection.

The procedure is similar to nuclear transference but the obtained embryo is not implanted in a surrogate mother but cultured in laboratory to produce induced pluripotent stem cells (IPS-cells) that will give origin to different cellular types according with the medium they were cultured.

Although reproductive cloning is banded by legislation all over the world, many countries, included Spain, have laws that regulate the research in therapeutic cloning. That is to say, cloning is allowed by law when the aim is cure a disease but not when it is the production of clones of an individual.

Animation: Induced pluripotent stem cells (IPS-cells)