Pleiotropy – An Overview and Related Disorders

‘PLEIOTROPY‘ term refers to the phenomenon in which a single locus affects two or more apparently unrelated phenotypic traits and is frequently identified as a single mutation affecting two or more wild-type traits. Pleiotropy comes from the Greek words pleio, which means “many,” and tropic, which means “affecting.” Pleiotropic genes are those that affect multiple, seemingly unrelated phenotypes. Pleiotropy should not be confused with polygenic traits, which occur when multiple genes interact to produce a single phenotype. Let’s have a glance at the topic of pleiotropy in detail.

What is Pleiotropy in Genetics?

In genetics, pleiotropy is characterised as the manifestation of numerous phenotypes by a single gene. Pleiotropy is a word with Greek roots that means “many ways”. A simple example of Pleiotropy is the disease phenylketonuria. It is a genetic disorder caused by a lack of phenylalanine metabolism in body cells. Gregor Mendel, the father of genetics, made many interesting observations about the colour of various plant components while studying inheritance. Mendel also noticed that plants with coloured seed coats had coloured leaf axils (the part of the leaf that connects to the stem) and coloured flowers. The colour of the seed coat and the colour of the axils, on the other hand, were the two different characteristics that Mendel observed to always be connected to the colours. The colour of the seed coat was always associated with the colour of the axil and flower.

Pleiotropy

We now know that Mendel’s observations were based on pleiotropy, which is the phenomenon in which an individual gene plays a role in multiple phenotypic traits. In this case, the gene responsible for seed coat colour was also responsible for axil pigmentation and flower colour. Marfan syndrome is a human genetic disorder caused by a single gene mutation, but it affects many aspects of growth and development, including vision, height, and heart function. All of these are examples of pleiotropy or a gene that influences multiple traits.

Gene Pleiotropy

Gene pleiotropy refers to a gene that focuses on the number of functions of a specific gene. It is also known as molecular-gene pleiotropy. When we think of Mendel’s experiments with white flowers and purple plants, we don’t think of phenotypes that are concerned with the colours of two flowers. Mendel, on the other hand, noticed that the colours were always related to two distinct features: the colour of the seed coat and the colour of the axils.

Plants with white flowers have colourless axils and seed coats, whereas plants with purple flowers have brown-grey seed coats with reddish axils. As a result, rather than affecting only one characteristic, the colour gene affects three. Pleiotropic genes are ones that regulate several distinct traits. Pleio refers to many, and tropic refers to effects. Hence, a deficiency in a single gene with several functions could be linked to different symptoms. Moreover, pleiotropic gene alleles are transmitted similarly to how single trait-affecting gene alleles are.

Human Genetic Disorders

The majority of the genes affected by human genetic disorders are pleiotropic. A person with Marfan syndrome, for example, may experience a variety of unrelated symptoms such as “Height is unusually tall” and “Lens dislocation of the eye”. The aorta, a large blood vessel that transports blood away from the heart, ruptures as a result of heart problems. The symptoms listed above do not appear to be related, but they can be traced back to a gene mutation. By encoding a protein into chains, these genes create fibrils that give the connective tissues of the body flexibility and strength. Marfan syndrome is caused by mutations that decrease the body’s production of functioning proteins, which leads to fewer fibrils.

Examples of Pleiotropy

• Sickle cell disease is an example of pleiotropy in humans. Sickle cell disease is caused by the formation of abnormally shaped red blood cells. Normal red blood cells have a biconcave, disc-like shape and contain massive amounts of haemoglobin. Haemoglobin aids red blood cells in binding to and transporting oxygen to the body’s cells and tissues. Sickle cell disease is caused by a mutation in the beta-globin gene. This mutation causes sickle-shaped red blood cells, which clump together and become stuck in blood vessels, obstructing normal blood flow. A single mutation in the beta-globin gene causes a variety of health problems and damages multiple organs, including the heart, brain, and lungs.
• Another disease caused by pleiotropy is phenylketonuria or PKU. PKU is caused by a mutation in the gene responsible for producing the enzyme phenylalanine hydroxylase. This enzyme degrades the amino acid phenylalanine, which is obtained from protein digestion. Without this enzyme, levels of the amino acid phenylalanine in the blood rise, causing neurological damage in infants. Infants with PKU disorder may experience intellectual disabilities, seizures, heart problems, and developmental delays.

FAQs on Pleiotropy

Q1: What type of inheritance is pleiotropy?

Answer:

Pleiotropy is a form of complicated genetic inheritance where one gene influences a variety of attributes. The genotype, or genetic makeup of an organism, governs the phenotype, or expressed trait.

Q2: What is the importance of pleiotropy?

Answer:

Pleiotropy is crucial to improving our knowledge of human biology and disease. Pleiotropy is prevalent in the human genome, according to the findings of genome-wide association studies (GWASs).

Q3: How can genes show pleiotropy?

Answer: 

Pleiotropy refers to when a genetic variation affects two or more attributes through separate biological pathways, such as when it affects different tissues or when it is causally linked to variation in another trait.

Q4: What is the common disease of pleiotropy?

Answer:

Marfan syndrome, which is brought on by a change in the FBN1 gene, serves as an illustration. Marfan syndrome patients frequently have long, thin fingers, toes, and limbs. But, they are also more likely to experience a wide range of symptoms, such as heart defects and issues with the eyes and spine.