Science is advancing, and knowledge in genetics and inheritance is becoming more and more accurate, allowing new discoveries in the human genome to be revealed. 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 pleiotropy , a phenomenon by which 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 pleiotropy.

Pleiotropism: what is it?

The word pleiotropism comes from the Greek “pleĂ­ĹŤn”, which means more, and “tropes”, which means change; the terms polyphene or multiple phenotypic expression are also used, although less so.

Pleiotropy appears when a single gene affects more than one phenotype , i.e. more than one phenotypic characteristic (e.g. eye colour, hair colour, height, freckles, etc.)

When genetics was first studied, back in the days of Mendel’s Laws, it was initially believed that each character or trait was controlled by a single gene. They later discovered that there were cases where the manifestation of a characteristic could require the participation of more than one gene, and conversely that the same gene could determine several traits (pleiotropy) .

History

The word “pleiotropy” was first used by a German geneticist, Ludwig Plate , in 1910.

Plate used the term to explain the appearance 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 inheritance

Pleiotropy is a concept that is specific to developmental genetics . Genetics is the part of biology that studies the genes and the mechanisms that regulate the transmission of hereditary traits. And, more specifically, developmental genetics is the part of genetics that specialises in characterising the causes of organisms developing in a particular way.

Genetic inheritance is the process by which the characteristics of individuals are passed on to their offspring. These characteristics are physiological, morphological and biochemical .

On the other hand, the concept of pleiotropy encompasses two other terms: genotype and 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 the genes that it inherits ; the genes contain the genetic information (or material) of the individual.

2. Phenotype

These are the “visible” characteristics that the person inherits from his parents, that is, the set of features of an individual . For example, the colour of the skin, the height, the shape of the ears, the 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 (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 from which pleiotropy is produced consists in that the same gene is activated in different tissues, producing different effects ; this is a very common phenomenon, since most genes have effects in more than one tissue.

Examples of pleiotropic diseases

As we have seen, pleiotropy 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 , that is, they are independent.

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

1. Sickle cell disease

Sickle cell anemia is caused by pleiotropism, and 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 disease is a genetic disorder; 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 a sickle cell trait.

2. Marfan Syndrome

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

Persons with this syndrome have an abnormality in the carpal bones and other bones in the front extremities. 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.