Deleterious comes from a Greek word that can be translated as “destroyer”. The term refers to that which is poisonous or deadly. For example: “Experts affirm that it is a deleterious insect for humans due to the toxicity of its venom “, “Aspiration of this type of substance produces a deleterious effect”, “He tried to remain calm, but soon realized that he was in a deleterious situation”.
The deleterious, therefore, is something harmful, dangerous, noxious or detrimental. Among its antonyms are concepts such as harmless or innocuous: “The blue substance that is in that container is harmless; the green substance, on the other hand, is deleterious”, “When we saw it for the first time, we thought it was a harmless reptile but, after analyzing its bite, we understood that it was deleterious”.
Deleterious or lethal genes are those that are subject to mutation or reorganization processes that cause alterations in their phenotypic expression. These genes come in different alleles (gene sequences) that produce changes in the individual. The deleterious or lethal allele is the one that carries the genetic sequence that causes death. The gene that, when mutated, can produce a lethal phenotype is known as the essential gene.
It is interesting that there are genes that prevent the correct reproduction of a species. Here are some of the possible reasons:
* Not all of them threaten biological fitness, as some of them begin their deleterious effects later than the most propitious time for reproduction. A clear example is the gene that causes Huntington’s disease (a neuropsychiatric disorder that generally affects people over 40 years of age), since the recommended age limit for human procreation is around 35 years;
* some are advantageous when only one copy is available, and for that reason natural selection cannot completely eliminate them. Such is the case of the gene that produces sickle cell anemia, since when you have two copies of it, resistance against malaria increases;
* mutation can keep them present, even if natural selection tries to eliminate them little by little. Neurofibromatosis, for example, is a genetic disease that produces tumors in our nervous system, and the gene that causes it mutates frequently (probably in one sexual cell in 4,000), so it is not possible to get rid of it completely;
* if the gene is not harmful in a habitat, it tends to appear more frequently than where it produces clearly unfavorable effects. Returning to the example of the gene that causes sickle cell anemia, it is logical that it occurs very often in people living in areas with a high probability of contracting malaria, since it is beneficial to them. The problem begins with migration, which carries deleterious genes to all parts of the planet;
* Perhaps natural selection has not completed its fight against certain genes. One reason for such ‘slowness’ is that a gene may be beneficial to a population at one point in history, but become harmful later on. When the organism no longer needs a gene to survive, it cannot discard it immediately, but rather evolution seeks a way to eliminate it throughout future generations.
The notion of deleterious is usually linked to an effect or a consequence. Something can be deleterious when it carries the possibility of serious harm, death, or destruction. Toxic substances, in this sense, are deleterious, although with different degrees. The higher the toxicity, the more deleterious they are. The science that studies the deleterious effect of substances on living beings is known as toxicology.