The genetic make-up of an organism can be changed randomly and "naturally" or artificially in a targeted way. The first phenomenon occurs between individuals of the same species through crossing-over. Furthermore, in bacteria, it can take place between different cells due to the processes of transduction, conjugation, and transformation. On the other hand, if the genetic structure of an organism is artificially altered, it is called biotechnology.
Gene exchange between alleles typically occurs during sexual reproduction. The resulting new genotypes significantly extend the genetic variability of a population. Recombination is a relatively random process. Genetic stability, i.e., the conservation of DNA sequences in generations, is crucial for the survival of individuals and species. It is crucial. The ability of DNA is to undergo ‘reassortments’ can vary the particular combination of genes present in each individual genome. Forms of gene recombination are also present in bacteria, viruses, plasmids, and mitochondria; precisely in these systems, in which DNA is not bound to proteins, it has been possible to better understand the recombinative process. Thus, general recombination and site-specific recombination were distinguished. In general recombination, genetic exchange occurs between pairs of homologous DNA sequences.
The recombination events are represented by the breakdown of two double-helix DNA molecules in sites exactly corresponding to the homologous chromosomes, by the exchange of both filaments and by the reconstruction of the double helixes by joining the free ends. The whole process is so accurate that the number of nucleotides in the recombined filaments remains the same. One of the most important examples of recombination in sexually reproduced organisms occurs during the meiotic process, through recombination. They are represented by the breakdown of two double-helix DNA molecules in sites exactly corresponding to the homologous chromosomes, by the exchange of both filaments and by the reconstruction of the double helixes by joining the free ends. The whole process is so accurate that the number of nucleotides in the recombined filaments remains the same.
Transduction is performed by a phage that transfers a part of the DNA of a bacterium to another bacterial cell; a phage that has infected a bacterium can incorporate portions of its DNA and introduce it into the chromosome of another bacterium that it has subsequently infected.
In conjugation, DNA passes from one bacterium to another with which it comes into contact by means of a cytoplasm filament. The cells produced by the division of the bacterium that received the DNA will have a reassorted chromosome since it also derives from the other bacterium.
The transformation consists of the passage from one bacterium to another of a plasmid, that is, of the DNA supplementary to its chromosome; the plasmid carries the genes that help develop antibiotic resistance.
Biotechnologies are those techniques that allow producing both substances and services (for example, analysis, water purification, etc.) with the use of living organisms, cells and their constituents, or through their genetic manipulation.
Properly, the techniques that allow altering the genetic heritage of organisms are called genetic engineering. Unlike natural recombination, genetic engineering alters the genome of an organism in a targeted way, isolating some of its genes (possibly modified) and inserting them into cells of another species, where they multiply and synthesize their proteins. The host cell (in which to introduce genes) is normally a bacterium. The advantages in the use of bacteria are manifold, simplicity of the cell, knowledge of natural recombination mechanisms, growth rate.
Biotechnology has been used for millennia to produce wine, cheese, and fermented products in general. However, they took on great importance only in the 80s after, with the discovery of DNA and the genetic code, the functioning of genes was understood, and the recombinant DNA technique was perfected. Currently, biotechnology is used in health care (production of substances that are the basis of drugs), in agriculture (insertion of particular genes useful in the genome of plants), in nutrition (product processing, quality and status control of food preservation) and in the defense of the environment (waste treatment, water purification).
One of the most important methodologies of genetic engineering uses recombinant DNA. This technique uses restriction enzymes, capable of cutting bacterial and human DNA in correspondence of precise sequences so that the ends of the two chains are complementary and can pair.
The recombinant DNA molecule is formed when DNA-ligase molecules firmly weld the ends of human DNA to those of bacterial DNA. The recombinant DNA is then introduced into a bacterial cell, where it produces the protein corresponding to the inserted human gene. As it reproduces by cell division, a clone of genetically identical cells is formed, endowed with recombinant DNA.
An alternative method to cloning to obtain large quantities of recombinant DNA uses the polymerase chain reaction.
The polymerase is an enzyme capable of synthesizing sequences of macromolecules starting from monomers. For example, DNA polymerase synthesizes DNA from nucleotides. The polymerase chain reaction technique manages to activate in the test tube the same DNA replication process that occurs in the cell.
Starting from a known sequence, two DNA primers are synthesized in the laboratory, about twenty nucleotides long, complementary to the two strands of DNA to be amplified. At this point, a cycle of reactions is repeated several times which consists of three phases:
1. Denaturation: the two strands of DNA to be amplified is separated by means of heat.
2. Hybridization: these two strands match the DNA primer molecules.
3. Extension: using free nucleotides, the DNA polymerase copies one of the two filaments starting from the primer; the synthesized DNA will be complementary to that of origin.
It is also called factorial recombination, the new distribution of an individual's genetic material that occurs spontaneously following an exchange of genes between various elements of the same molecule or between two different DNA molecules.
There are various types of recombination, distinguished according to the cells involved (sexual or otherwise) and at the time when the phenomenon occurs.
Meiotic recombination also called crossing over; it derives from an exchange of genes in a sex cell. It occurs between two chromosomes of the same pair during meiosis, a process during which a sex cell with 46 chromosomes divides, giving rise to two new cells with 23 chromosomes each. This phenomenon causes the mother and daughter cells to exhibit a different chain of genetic characteristics and the genes that transmit them.
Recombination between chromatids occurs during the division of a cell. It is the result of an exchange of genes between the two chromatids of the same chromosome (i.e., between the two parts of the chromosome which are united by the centromere before cell division).
Recombination within the same DNA molecule is produced following cell division in the elements that previously formed the same chromosomes.