Pleiotropism is a phenomenon studied by genetics, and it explains many traits and diseases.
Science advances, and knowledge in genetics and inheritance is becoming more exact, allowing the unveiling of new findings in the human genome. For its part, genetics studies genes and how we inherit the characteristics that our parents transmit to us.
In this article we will see what pleiotropism is, a phenomenon by which a single gene affects various phenotypic traits in the same organism, usually not related to each other. We will know the differences between genotype and phenotype, and some examples of pleiotropism.
Pleiotropism – what is it?
The word pleiotropism comes from the Greek “pleíōn”, which means more, and “tropos”, which means change; the terms polyphenia or multiple phenotypic expression are also used, although less.
Pleiotropism appears when a single gene affects more than one phenotype, that is, more than one phenotypic characteristic (for example, eye color, hair color, height, freckles, etc.)
When genetics began to be studied, already at the time of Mendel’s Laws, at first it was believed that each character or trait was controlled by a single gene. Later they discovered that there were cases in which the manifestation of a character could require the participation of more than one gene, and on the contrary, that the same gene could determine different traits (pleiotropy).
The word “pleiotropy” was first used by a German geneticist, Ludwig Plate, in 1910.
Plate used the term to explain the appearance of several different phenotypic traits that always occur together and that can appear to be correlated. According to him, the fact that this happened was due to a unit of pleiotropic inheritance.
Genetics and human inheritance
Pleiotropism is a concept of developmental genetics. Genetics is the part of biology that studies genes and the mechanisms that regulate the transmission of hereditary characters. And, more specifically, developmental genetics is the part of genetics specialized in characterizing the causes for which organisms develop in a particular way.
Genetic inheritance is the process by which the characteristics of individuals are transmitted to their offspring. These characteristics are physiological, morphological, and biochemical.
On the other hand, the concept of pleiotropism encompasses two other terms: genotype and phenotype.
It is the set of non-visible characteristics that a living being inherits from its parents. That is, it would be the set of all the genes it inherits ; genes contain the genetic information (or material) of the individual.
These are the “visible” characteristics that the person inherits from their parents, that is, the set of traits of an individual. For example skin color, height, ear shape, facial features, etc. The phenotype arises as a result of the interaction between the genotype of a person and her environment.
The phenotype includes not only physical traits, but also behavioral traits (eg impulsivity, patience, temperament, etc.).
3. Differences between the two
Thus, the difference between genotype and phenotype is that the genotype can be distinguished by looking at DNA, and the phenotype is known by observing the external appearance of an organism.
How does pleiotropy occur?
The mechanism from which pleiotropism occurs is that the same gene is activated in different tissues, producing different effects ; This is a very common phenomenon, as most genes have effects on more than one tissue.
Examples of pleiotropic diseases
As we have seen, pleiotropism is the condition in which the mutation in a single gene affects multiple phenotypic characteristics in the same organism. Often these pleiotropic effects or phenotypic characteristics are unrelated to each other, that is, they are independent.
Some examples of pleiotropism in humans are sickle cell anemia, Marfan syndrome, and Holt-Oram syndrome.
1. Sickle cell anemia
Sickle cell anemia appears due to pleiotropism, and it is a hereditary disease that affects hemoglobin, a protein that is part of red blood cells and is responsible for oxygen transport. In this case, the body produces abnormally shaped red blood cells (sickle).
Sickle cell anemia is the product of a genetic alteration; People with the disease are born with two sickle cell genes, one from each parent. The presence of the sickle cell gene and another normal gene is called sickle cell trait.
2. Marfan syndrome
Marfan Syndrome, also a case of pleiotropism, consists of a disease that affects the connective tissue. A series of skeletal, ocular, and cardiovascular abnormalities occur in the body, all of which are based on a defect in fibrillin in the connective tissue.
All of these symptoms are directly related to the mutation of a single gene, the FBN1 gene, which is pleiotropic. The function of this gene is to encode a glycoprotein that is used in connective tissues in different parts of the body.
3. Holt-Oram syndrome
People with this syndrome have an abnormality in the carpal bones and other bones of the forelimbs. In addition, about 3 out of 4 patients with Holt-Oram syndrome also have heart problems.
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