Pleiotropism: what it is and how it affects people's traits

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

In this article We will see what is pleiotropism, a phenomenon whereby a single gene affects several phenotypic traits in the same organism, usually unrelated to each other. We will know the differences between genotype and phenotype, and some examples of pleiotropism.

• Related article: "Genetics and behavior: do genes decide how we act?"

Pleiotropism: what is it?

The word pleiotropism comes from the Greek “pleíōn”, which means more, and “trópos”, which means change; The terms polypheny or multiple phenotypic expression are also used, although less often.

Pleiotropism appears when a single gene affects more than one phenotype, that is, to 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 the

Mendel's lawsAt 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).

History

The word "pleiotropy" it was first used by a German geneticist, Ludwig Plate, in 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 unit of pleiotropic inheritance.

Genetics and human heredity

Pleiotropy 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, development 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: the genotype and the phenotype.

1. Genotype

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 genes inherited; genes contain the genetic information (or material) of the individual.

2. phenotype

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 a person's genotype and their environment.

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

3. Differences between the two

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

How does pleiotropy occur?

The mechanism by 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 in more than one tissue.

Examples of Pleiotropic Diseases

As we have seen, pleiotropism is the condition in which a mutation in a single gene affects multiple phenotypic characteristics in the same organism. Often these pleiotropic effects or phenotypic features 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

Sickle cell anemia appears by pleiotropism, and it is a hereditary disease It affects hemoglobin, a protein that is part of red blood cells and is responsible for transporting oxygen. In this case, the body produces red blood cells with an abnormal shape (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 one sickle cell gene and one normal gene is called sickle cell trait.

2. Marfan syndrome

Marfan Syndrome, also a case of pleiotropism, consists of a disease that affects connective tissue. A series of skeletal, ocular and cardiovascular abnormalities occur in the body, which have as a common base a defect in the fibrillin of the connective tissue.

All these symptoms are directly related to a single gene mutation, 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. Also, 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.
• Wolf, 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.
• Sanchez Elvira Paniagua, A. (2005). Introduction to the study of individual differences. Madrid: Ed. Sanz y Torres. 2nd Edition.