Cloning is a propagation mechanism carried out by organisms that have asexual reproduction, such as some species of bacteria, hydras, among others. In asexual reproduction , a single individual originates its descendants, that is, there is no exchange of genetic material with another organism, thus, all descendants are identical to the organism that generated them, being called clones.
Clones can be defined as a set of molecules, cells or organisms that originated from a single cell, being identical to it. Some plant species can produce clones through budding or reproduction by cuttings , for example. In the human species, identical twins or identical twins can be considered clones, as they originate from the same fertilized egg and carry an identical genetic heritage.
Cloning does not only occur naturally, it is also carried out through laboratory processes . These processes produce everything from identical copies of some molecules, such as DNA, to organisms. One of the most emblematic cases of organism cloning was carried out in 1996 and which gave rise to Dolly the sheep .
Dolly originated from the introduction of the nucleus removed from mammary gland cells of Finn-dorset ewes into oocytes, whose nuclei had been removed, from the Scottish black-face breed . Dolly was the only one of the 247 embryos generated that developed. She was a clone of the Finn-Dosset race and had originated from an adult cell, which was a great novelty in cloning studies.
How is cloning performed?
As previously mentioned, natural cloning occurs through processes of asexual reproduction , in which there is no exchange of genetic material between individuals, and only one organism gives rise to another, which is identical to the parent. In laboratory processes , the techniques used vary according to the purpose of the procedure.
types of cloning
Below we present some types of cloning performed, their objectives and how they are performed.
1. Reproductive cloning
This type of cloning aims to produce organisms identical to the parent . The technique, which is called nuclear transfer, basically consists of removing the nucleus from an adult cell and introducing it into an egg from which the nucleus has been removed and, therefore, no longer has genetic material. This cell is then transferred to the organism’s uterus , which will continue the development of the embryo. This was the procedure performed for the creation of Dolly the sheep.
However, this type of cloning presents some problems, such as the early death of the clones and the presence of abnormalities possibly caused by failures in the reprogramming of the genome. Reproductive cloning is more effective when performed by transferring embryonic cell nuclei instead of adult cell nuclei.
2. Therapeutic cloning
Therapeutic cloning is performed using a procedure similar to reproductive cloning, in which DNA from an adult cell is removed and introduced into an egg without the presence of genetic material. However, unlike reproductive cloning, the cell is not introduced into a uterus to grow. After a few divisions, the stem cells (cells with a great capacity for division and differentiation, thus being able to become other cell types) are directed towards the formation of tissues identical to those of the donor .
Therapeutic cloning could be used in the treatment of some diseases – such as heart problems, in order to replace heart tissue after a heart attack – or in transplants . With this technique, rejection problems would be reduced, since the material used in the treatment would have been produced from the diseased organism.
Some points, however, deserve attention. If the patient has a genetic disease , for example, he could not be your donor, since the disease-causing mutation would be present in all cells. In the case of using cells from another donor, the recipient could present rejection, leading the body to produce antibodies against these cells.
Importance and limitations of cloning
Cloning is a very important procedure, as it opens up perspectives, for example, for treatments that require transplants , through the cultivation of cells identical to those of the tissue from which they were taken. Reproductive cloning can also be a hope for couples who cannot have children due to genetic problems , for example.
However, all these techniques come up against some limitations , requiring further studies on their possible results and consequences. The use of embryonic cells in some processes is one of the main problems faced, as many consider that cells are being removed from “potential people”, leading to debates about the ethical and moral limits of carrying out some procedures.
Some techniques, such as therapeutic cloning , still require further studies so that they can be applied in clinical treatment. Therefore, the use of stem cells from other sources, such as those from the umbilical cord , is the most promising technique in the short term.
Other techniques, such as reproductive cloning, face ethical, cultural and religious problems . Reproductive cloning, for example, is rejected practically all over the world, especially when we talk about the use of this technique in human beings. However, in other animal species, it has been useful for understanding cell functioning.