Cloning is the creation of an organism or a group of organisms from one cell. In the scientific argot, it is also called nuclear transference.
The organism created by means of this technique is called a Clone.
The reproduction of bacteria in a Petri dish is a good example on cloning.
The clone is almost a perfect replica of the organism from which the DNA (molecules that contain the genetic code) was obtained.
The complete genetic material of an organism is called Genome. Regularly, the genetic material is found in the cell nucleus (bacteria have not a well-differentiated nucleus), but part of the genetic material is located in mitochondria, not in nucleus.
The cloning of animals with sexual reproduction is performed by extracting the nucleus of a somatic cell (any body cell, except gametes) and removing the nucleus from an ovum (female gamete, or reproductive cell) (see note). Then, the nucleus of the somatic cell is transferred into the enucleated (without nucleus) ovum, that is to say, the ovum from which we had removed the nucleus.
This can be achieved through two techniques:
- Through an electric discharge, or
- By the injection of the somatic cell's genetic material inside the enucleated ovum (an ovum without nucleus) through "micro-syringes".
The result of this procedure is called an egg, or a zygote.
Then, the created egg is induced to replication, until the development of a small embryo (blastula) is completed, which already can be implanted in the uterus (womb) of a host mother (she who lends her uterus to contain the embryo), or the uterus of the same mother who provided the ovule (Donor).
In primitive organisms (at a low evolutionary level, like amphibious and reptiles), cloning is reasonably uncomplicated. In upper organisms, as human beings, cloning is remarkably complex. For example, by each 100 cloned cells, only ten cells survive; from these 10 cells, only seven cells develop to blastulae (blastulas); of these seven cells, only one grows inside the mother. Of each 1000 embryos, only one is born plausibly in good physical shape.
As we see, cloning of mammals is highly difficult. However, it can be realized. Troubles enlarge when cloning deals with human beings.
If a human clone is obtained from a somatic cell of a different person from the donor of ova (pl. of ovum), the obtained clone will be genetically different from the donor; therefore, the ovum's mitocondrial DNA of the donor will have an effect on clone's phenotype. If the donor of the somatic cell is the same person who provided the ovum, then the clone will be virtually identical to the donator.
The problems that can take place in cloning are:
- The inheritance of genetic damages suffered in the donor's DNA, through his/her life.
- The reception of aged genetic material from the donor of the somatic nucleus when donation is made (it leads the clone to a hasty ageing).
- The deletion, transposition, or alteration of genes during the manipulation of the genetic material.
- The addition by transference of strange genes, different to the original genome, because of the contamination of the environment where the created cells are cultivated.
Note: It is more proper to call "Ovum" than "Egg" to an unfertilized female gamete. The concept "Egg" describes a fertilized female gamete.