DNA cloning means producing countless identical copies of the same fragment of the DNA molecule. This process begins with the isolation, by the action of restriction enzymes, of fragments of DNA to be cloned. Once isolated, these stretches are introduced into the DNA of other organisms, mainly viruses and bacteria, called vectors. Already the animal cloning in multicellular organisms, can happen through three techniques developed.
- Emergence of monozygotic twins. In this case, semen and ova are collected from selected animals that have characteristics of interest and promote fertilization. As soon as the zygote forms and the first cell divisions begin, the originated cells are artificially separated and implanted in females (“surrogate mothers”), where embryonic development is completed. These cells will give rise to genetically identical individuals. Then clones of animals of interest to humans are formed.
- From somatic cells, as was the case with Dolly the sheep : a recipient cell, the oocyte removed from the ovary of a Blackface sheep , had its genetic material removed with the aid of a micropipette. A cell (2n) removed from the mammary gland of an adult Finn Dorset sheep was kept in a state of quiescence, that is, in conditions that made it inactive. This cell was fused to the oocyte devoid of nuclear genetic material. The oocyte, now with the 2n nucleus received from the somatic cell, was stimulated to start embryonic development. Then, the embryo with few cells was introduced into the uterus of a “surrogate mother”.
See also : DNA – Chromosomes, genes, genome and RNA
- From embryonic cells, as was the case with the first animal cloned in Brazil : the heifer Vitória, of the Simental breed, which was born in 2001, at the Experimental Sucupira Field, of Embrapa. Vitória is the result of the transfer of the nucleus of a five-day-old embryo cell, collected from a Simenta cow, to an enucleated oocyte taken from a cow of another breed. Then, the embryo in the beginning of development was implanted in a “surrogate cow”. The pregnancy and delivery were successful and at the age of three, Vitória received the semen from a bull of her breed and gave birth on February 19, 2004 to her first calf: the heifer Glória.
Animal cloning can happen through three techniques developed (Photo: depositphotos)
The possibility of human cloning has raised intense ethical discussions. Human cloning for reproductive purposes, which is cloning for the purpose of obtaining an individual, is not permitted by law, but therapeutic cloning, which is done for the purpose of producing embryonic stem cells for therapeutic use, yes.
It is worth mentioning that individuals are not cloned, but genomes , that is, the set of all the nuclear DNA that a certain organism has in its cells.
Cloning does not prevent the complex interactions of the genotype with the environment in the production of the phenotype. Thus, despite being genotypically identical, the clones will not have exactly the same phenotypes. Another issue to be considered in these clones is mitochondrial DNA, which may contain some genes associated with diseases, such as the human disease called Leber’s optic atrophy, a type of blindness.
If cloning is done only with the transfer of 2n nucleus to the oocyte devoid of nuclear DNA, the mitochondrial DNA will be that of the oocyte and the clone will not be complete due to the genetic material of the mitochondria.
When fusion occurs between the 2n cell and the oocyte devoid of nuclear DNA, the mitochondrial DNA is part of the oocyte and part of the somatic cell and the clone will have mitochondria from both the oocyte and the cell that fused to it. Maternity tests can be done by analyzing mitochondrial DNA, as the descendants’ mitochondria are inherited only from the mother.