HUMAN CLONING: METHODS, STAGES, ADVANTAGES, DISADVANTAGES - BIOLOGY - 2025

The human cloning refers to the production of identical copies of an individual. The term derives from the Greek roots of the "asexual replication of an organism." The production of clones is not a process restricted to the laboratory. In nature, we see that clones are generated naturally. For example, bees can be propagated by clones of the queen bee.

This procedure is very useful in the biological sciences, with functions that go beyond producing one human identical to another. Cloning is not only used to create two identical organisms, it also involves the cloning of tissues and organs.

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These organs will not be rejected by the patient's body, since they are genetically the same as it. Therefore, it is an applicable technology in the field of regenerative medicine and is a very promising alternative in terms of curing diseases. The two main methods used in cloning are somatic cell nuclear transfer and induced pluripotent stem cell.

Generally speaking, it is a subject of significant controversy. According to experts, human cloning carries a series of negative consequences from the moral and ethical point of view, together with the high mortality rates of the cloned individuals.

However, with the advancement of science, it is possible that in the future cloning will become a routine technique in laboratories, both for curing diseases and assisting in reproduction.

Definition

The term "human cloning" has been surrounded by much controversy and confusion over the years. Cloning can come in two forms: a reproductive one and a therapeutic or investigational one. Although these definitions are not scientifically correct, they are widely used.

Therapeutic cloning is not intended to create two genetically identical individuals. In this modality, the end goal is the production of a cell culture that will be used for medical purposes. By means of this technique, all the cells that we find in the human body can be produced.

In contrast, in reproductive cloning, the embryo is implanted into a female for the gestation process to take place. This was the procedure used for the cloning of Dolly the sheep in July 1996.

Note that, in therapeutic cloning, the embryo is cultured from the stem cells, rather than brought to term.

On the other hand, in genetics and molecular biology laboratories, the word cloning has another meaning. It involves the taking and amplification of a DNA segment that is inserted into a vector, for its subsequent expression. This procedure is widely used in experiments.

Cloning history

The current processes that allow the cloning of organisms are the result of hard work by researchers and scientists for more than a century.

The first sign of the process occurred in 1901, where the transfer of a nucleus from an amphibian cell was transferred to another cell. In the following years, scientists succeeded in cloning mammalian embryos - roughly between the 1950s and 1960s.

In 1962 the production of a frog was achieved by transferring a nucleus of a cell taken from the intestine of a tadpole to an oocyte whose nucleus was removed.

Dolly the sheep

In the mid 1980's cloning of sheep from embryonic cells was carried out. Likewise, in 1993 cloning was carried out in cows. The year 1996 was key to this methodology, since the most well-known cloning event in our society occurred: Dolly the sheep.

What was unique about Dolly to get media attention? Its production was carried out by taking differentiated cells from the mammary glands of an adult sheep, while previous cases had done so using exclusively embryonic cells.

In 2000, more than 8 species of mammals had already been cloned, and in 2005, a canid named Snoopy was cloned.

Cloning in humans has been more complex. Within history, certain frauds have been reported that have caused an impact on the scientific community.

Methods

Somatic cell nuclear transfer

Generally, the cloning process in mammals takes place by a method known as "somatic cell nuclear transfer". This was the technique used by researchers at the Roslin Institute to clone Dolly the sheep.

In our body, we can differentiate two types of cells: somatic and sexual. The former are those that form the "body" or tissues of the individual, while the sexual ones are the gametes, both the ovules and the sperm.

They differ mainly by the number of chromosomes, somatic ones are diploid (two sets of chromosomes) and haploid sexual ones contain only half. In humans, the body's cells have 46 chromosomes and the sex cells only 23.

Somatic cell nuclear transfer - as the name implies - consists of taking a nucleus from the somatic cell and inserting it into an egg whose nucleus has been removed.

Induced pluripotent stem cell

Another method, less efficient and much more laborious than the previous one, is the "induced pluripotent stem cell". Pluripotent cells have the ability to give rise to any type of tissue - in contrast to a common cell in the body, which has been programmed to fulfill a specific function.

The method is based on the introduction of genes called "reprogramming factors" that restore the pluripotent capacities of the adult cell.

One of the most important limitations of this method is the potential development of cancer cells. However, progress in technology has improved and reduced possible damage to the cloned organism.

Stages (in main method)

The steps for somatic cell nuclear transfer cloning are very simple to understand and comprise three basic steps:

Components required for cloning

The cloning process begins once you have two types of cells: a sexual and a somatic.

The sex cell must be a female gamete called an oocyte - also known as an egg or ovum. The egg can be harvested from a donor who has been treated hormonally to stimulate the production of gametes.

The second type of cell must be a somatic, that is, a cell of the body of the organism that you want to clone. It can be taken from liver cells, for example.

Core transfer

The next step is to prepare the cells for the transfer of the nucleus from the donor somatic cell to the oocyte. For this to occur, the oocyte must be devoid of its nucleus.

To do this, a micropipette is used. In 1950 it was possible to show that, when an oocyte was punctured with a glass needle, the cell underwent all the changes associated with reproduction.

Although some cytoplasmic material may pass from the donor cell to the oocyte, the contribution of the cytoplasm is almost total by the ovum. Once the transfer has been carried out, this ovum must be reprogrammed with a new nucleus.

Why is a reprogramming necessary? Cells are capable of storing their history, in other words it stores a memory of their specialization. Therefore, this memory must be erased so that the cell can specialize again.

Reprogramming is one of the biggest limitations of the method. For these reasons, the cloned individual appears to have premature aging and abnormal development.

Activation

The hybrid cell needs to be activated for all developmental processes to occur. There are two methods by which this objective can be achieved: by electrofusion or Roslin method and by microinjection or Honolulu method.

The first consists of the use of electric shocks. Using the application of a pulse current or ionomycin the ovum begins to divide.

The second technique only uses pulses of calcium to trigger the activation. A prudent time is expected for this process to take place, approximately two to six hours.

Thus begins the formation of a blastocyst that will continue the normal development of an embryo, as long as the process has been carried out correctly.

Advantage

One of the major applications of cloning is the treatment of diseases that are not easy to cure. We can take advantage of our extensive knowledge in terms of development, especially the early stages, and apply it to regenerative medicine.

Cells cloned by somatic cell nuclear transfer (SCNT) contribute enormously to scientific research processes, serving as model cells to investigate the cause of disease and as a system for testing different drugs.

Furthermore, the cells produced by said methodology can be used for transplantation or for the creation of organs. This field of medicine is known as regenerative medicine.

Stem cells are revolutionizing the way we treat certain diseases. Regenerative medicine allows autologous stem cell transplantation, eliminating the risk of rejection by the immune system of the affected person.

In addition, it can be used for the production of plants or animals. Creating identical replicas of the individual of interest. It can be used to recreate extinct animals. Lastly, it is an alternative to infertility.

How does it work?

For example, suppose there is a patient with liver problems. Using these technologies, we can grow a new liver - making use of the patient's genetic material - and transplant it, thus eliminating any risk of liver damage.

At present, regeneration has managed to be extrapolated to nerve cells. Some researchers believe that stem cells can be used in the regeneration of the brain and nervous system.

Disadvantages

Ethical issues

The main disadvantages of cloning stem from the ethical opinions surrounding the procedure. In fact, many countries cloning is legally prohibited.

Since the cloning of the famous Dolly the sheep occurred in 1996, many controversies have surrounded the issue of this process applied in humans. Various academics have taken positions in this arduous debate, from scientists to lawyers.

Despite all the advantages that the process has, the people who are against it claim that the cloned human being will not enjoy average psychological health and will not be able to enjoy the benefit of having a unique and unrepeatable identity.

In addition, they argue that the cloned person will feel that they must follow a specific life pattern of the person who gave rise to them, so they could question their free will. Many consider that the embryo has rights from the moment of conception and, altering it means violating them.

Currently, the following conclusion has been reached: due to the poor success of the process in animals and the potential health risks they pose to both the child and the mother, it is unethical to attempt human cloning for safety reasons.

Technical problems

Studies carried out on other mammals have allowed us to conclude that the cloning process leads to health problems that ultimately lead to death.

By cloning a calf from genes taken from the ear of an adult cow, the cloned animal suffered from health problems. At just two months old, the young calf died of heart problems and other complications.

Since 1999, researchers have been able to note that the cloning process leads to interference with the normal genetic development of individuals, causing pathologies. In fact, the cloning of sheep, cows, and mice reported has not been successful: the cloned organism dies shortly after birth.

In the famous case of the cloning of Dolly the sheep, one of the most prominent drawbacks was premature aging. The donor of the nucleus used to create Dolly was 15 years old, so the cloned sheep was born with characteristics of an organism of that age, leading to rapid deterioration.

References

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3. Langlois, A. (2017). The global governance of human cloning: the case of UNESCO. Palgrave communications, 3, 17019.
4. McLaren, A. (2003). Cloning. Editorial Complutense.
5. Nabavizadeh, SL, Mehrabani, D., Vahedi, Z., & Manafi, F. (2016). Cloning: A Review on Bioethics, Legal, Jurisprudence and Regenerative Issues in Iran. World journal of plastic surgery, 5 (3), 213-225.