Pleiotropism: what is it and how does it affect people’s traits?

Pleiotropism is a phenomenon studied by genetics, and explains many traits and diseases.

Science is advancing, and knowledge in genetics and heredity is becoming more and more accurate, allowing new discoveries to be made in the human genome. Genetics studies genes and how we inherit the characteristics that our parents pass on to us.

In this article we will see what pleiotropism isPleiotropism, a phenomenon whereby a single gene affects several phenotypic traits in the same organism, normally unrelated 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", meaning more, and "trópos", meaning change; the terms polyphenia or multiple phenotypic expression are also used, although less frequently.

Pleiotropism occurs when a single gene affects more than one phenotype, i.e. more than one phenotype.that is, more than one phenotypic characteristic (e.g. eye color, hair color, height, freckles, etc.).

When genetics began to be studied, already at the time of Mendel's Laws, it was initially believed that each character or trait was controlled by a single gene. Later it was 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 several traits (e.g., the same gene could determine several traits). the same gene could determine several traits (pleiotropy)..

History

The word "pleiotropy was used for the first time by a German geneticist, Ludwig Platein 1910.

Plate used the term to explain the occurrence of several distinct phenotypic traits that always occur together and may appear to be correlated. According to him, the fact that this occurred was due to a pleiotropic unit of inheritance.

Genetics and human inheritance

Pleiotropism is a concept specific to developmental genetics.. Genetics is the part of biology that studies genes and the mechanisms that regulate the transmission of hereditary traits. More specifically, developmental genetics is the part of genetics specialized in characterizing the causes by 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.

1. Genotype

This is the set of non-visible characteristics that a living being inherits from its progenitors. In other words, it would be the set of all the genes that it inheritsThe genes contain the genetic information (or material) of the individual.

Phenotype

This refers to the "visible" characteristics that the person inherits from its progenitors, i.e, the set of traits of an individual. For example, skin color, height, shape of the ears, facial features, etc. The phenotype arises as a result of the interaction between a person's genotype and his environment.

The phenotype includes not only physical traits, but also behavioral traits (e.g. impulsiveness, patience, temperament, etc.).

3. Differences between the two

Thus, the difference between genotype and phenotype is that the genotype can be distinguished by observing the DNA, and the phenotype is known by observing the external appearance of an organism.

How does pleiotropy occur?

The mechanism by which pleiotropism is produced is that the same gene is activated in different tissues, producing different effects.Pleiotropism is a very common phenomenon, since most genes have effects in more than one tissue.

Examples of pleiotropic diseases

As we have seen, pleiotropism is the condition in which 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, i.e., they are independent.that is, they are independent.

Some examples of pleiotropism in humans are sickle cell anemia, Marfan syndrome and Holt-Oram syndrome.

Sickle cell anemia

Sickle cell anemia occurs due to pleiotropism, and is an inherited disease which affects hemoglobin, a protein that is part of red Blood cells and is responsible for oxygen transport. In this case, the body produces red blood cells with an abnormal shape (sickle).

Sickle cell disease is the result of a genetic disorder; people with the disease are born with two sickle cell genes, one from each parent. The presence of the sickle cell gene and a normal gene is called sickle cell trait.

2. Marfan syndrome

Marfan syndrome, also a case of pleiotropism, is a disease affecting the connective tissue. A series of skeletal, ocular and cardiovascular anomalies are produced in the organism, which have as common base a defect in the connective tissue.The common basis is a defect in the fibrillin of the connective tissue.

All These symptoms are directly related to the mutation of a single gene.FBN1 gene, which is pleiotropic. The function of this gene is to encode a glycoprotein that is used in connective tissues of different parts of the body.

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.

Bibliographic references:

• Brooker, R. J. (2017). Genetics: Analysis and Principles. McGraw-Hill Higher Education, New York, NY, USA.
• Lobo, I. (2008). Pleiotropy: one gene can affect multiple traits. Nature Education, 1-10.
• Nitxin, A., Araneda, C., Pascual, L., Barbadilla, A. and Carballo, M.A. (2010). Extensions to Mendelian principles: Pleiotropy.
• Sánchez Elvira Paniagua, A. (2005). Introduction to the study of individual differences. Madrid: Ed. Sanz y Torres. 2nd Edition.