Genes

We explain what genes are, how they work, what their structure is like and how they are classified. Genetic manipulation and mutations.

What are genes?

In biology, genes are known as the smallest unit of genetic information contained in DNA of a living being. All genes together form the genome, that is, the genetic information of the species.

Each gene is a molecular unit that encodes a specific functional product such as a protein. At the same time, it is responsible for transmitting said information to the organism's offspring, that is, is responsible for the inheritance.

The genes are found within the chromosomes (which in turn make life in the nucleus of our cells). Each gene occupies a specific position, called locusalong the gigantic sequential chain that makes up DNA.

Seen another way, a gene is nothing more than a short segment of DNA, which is found within the chromosome always located in the same place, since they usually occur in matched pairs (known as alleles). That means that for each specific gene there is another allele a copy.

The latter is very important in inheritance since some physical or physiological traits can be dominant (they tend to manifest) or recessive (they do not tend to manifest). The former are so powerful that one gene from both alleles is enough to manifest, while the latter require that the two alleles be identical to manifest.

However, recessive genetic information can be inherited, since a person who does not manifest a specific gene can still pass it on to their offspring. This is what happens when someone with dark eyes has a child with light eyes, usually like one of their grandparents.

As will be seen, the information contained in genes can determine many of our physical traits such as height, hair color, etc. But it can also cause congenital diseases or defects, such as trisomy 21 or Down syndrome.

History of genes

The father of the concept of inheritance was the Austro-Hungarian naturalist and monk Gregor Johann Mendel (1822-1884), who determined in his studies that there was a set of specific traits that were heritable from one generation to another.

Its appearance depended on what he called “factors” and which today we know as genes. Mendel assumed that these factors were arranged linearly in the chromosomes of cells, which had not yet been studied in depth.

However, In 1950, the shape and structure of DNA was discovered, in its famous double helix. Thus the idea prevailed that these factors, now called “genes”, were nothing more than a coding fragment of the DNA sequence, the result of which was the synthesis of a specific polypeptide, that is, a fragment of a protein.

With this discovery genetics is born and the first steps are taken towards knowledge and manipulation of the genetic code.

How do genes work?

Genes operate like a template or a pattern (according to the genetic code), which determines the type of molecules and the place where they should go, in order to compose a macromolecule endowed with specific functions within the organism.

Seen this way, the genes are part of the manufacturing mechanisms of life itself. It is a complex and self-regulated process, since various segments of the DNA itself operate as signals to start, end, increase or silence the transcription of gene content.

Types of genes

Genes are differentiated according to their specific role in protein synthesis, as follows:

• Structural genes Those that contain the coding information, that is, that which corresponds to the set of amino acids to form a specific protein.
• Regulatory genes Genes that lack coding information, but instead fulfill regulatory and ordering functions, thus determining the place of beginning and end of genetic transcription, or fulfill specific roles during mitosis and meiosis, or that denote the place where they should enzymes or other proteins combine during synthesis.

Structure of a gene

Genes are, from a molecular point of view, little more than a sequence of the nucleotides that make up DNA or RNA (adenine, guanine, cytosine and thymine or uracil). Its specific order corresponds to a specific set of amino acids, thus forming a macromolecule with a specific function (proteins, for example).

However, the genes are made up of two parts of different functions, which are:

• Exons The region of the gene that contains the coding DNA, that is, the specific sequence of nitrogenous bases that allow a protein to be synthesized.
• Introns The region of the gene that contains non-coding DNA, that is, it does not contain instructions for protein synthesis.

A gene can have a different number of exons and introns, and in some cases, such as the DNA of prokaryotic organisms (structurally simpler than that of eukaryotes), genes lack introns.

Genetic mutations

During the process of transcription of the genetic information of DNA, and its recomposition into a new protein, or also during the stages of DNA duplication and replication in cellular reproduction, it is possible, although not very common, for errors to occur.

One amino acid replaces another within a protein, as a consequence, and depending on the type of substitution and the place in the macromolecule where the substitute amino acid is located, it is possible that it is a harmless error, or that it triggers diseases, illnesses or even benefits. unexpected. To this type of spontaneous errors are known as mutations.

The mutations occur spontaneously and play an important role in inheritance and evolution. A mutation can provide a species with an ideal trait to better adapt to its environment, thus being favored by natural selection, or on the contrary, it can provide it with an unfavorable trait and lead to extinction.

Only those positive traits spread through the species as the favored individual reproduces more than others, eventually giving rise to a new species.

Genome

The genome is the set of all the genes contained in the chromosomes, that is, the totality of the genetic information of an individual or a species determined.

The genome is also the genotype, that is, the invisible and hereditary expression that largely produces the physical and physiological traits (the phenotype). The origin of this term comes from the union of “gene” and “chromosome”.

In diploid cells (2n), that is, in which there are pairs of homologous chromosomes, the complete genome of the organism is found in two entire copies, while in haploid cells (n) only one copy is found.

The latter is the case of gametes or sexual cells, which provide half of the genetic load of a new individual, completing it with that of the other gamete (male and female) to build a new genetically new individual.

Genetic engineering and gene therapy

As more and more has been learned about the functioning of genes, the genome of entire species has been decoded and technological tools are available to intervene in genetic information.

Currently, new biotechnological options have been born, such as genetic engineering (or genetic manipulation) and gene therapy, to name two famous cases.

Genetic engineering pursues the “programming” of organisms living things by manipulating (addition, deletion, etc.) their genetic code. For this, nanotechnology or some genetically manipulated viruses are used.

Thus, it is possible to obtain animal or plant species with a desired phenotype, in a more extreme version of selective reproduction (something we do with domestic animals). genetic engineering plays an important role in the food industry, in agriculture, livestock etc.

For its part, Gene therapy is a medical method of attacking incurable diseases such as cancer or hereditary, such as Wiskott-Aldrich Syndrome. It consists of the insertion of elements into the genome of an individual, directly into their cells or tissues.

For example, in the case of tumors, “suicidal” genes are introduced into abnormal cells that lead them towards their own disintegration, causing the cancer to eliminate itself by reproducing. This technique, however, is still in the experimental and/or initial phases.

References

• “Gene” on Wikipedia.
• “Genetic mutation” in Wikipedia.
• “What are genes?” in Imegen.
• “Genes” in MedlinePlus.
• “Genes and chromosomes” in MSD Manual.
• “What is a gene?” in Genetics Home Reference from the US National Library of Medicine.
• “Genes vs. DNA vs. Chromosomes” (video) in Scientific American.
• “Gene (heredity)” in The Encyclopaedia Britannica.