Introduction About What is Pleiotropy

Pleiotropy can be defined as the expression of multiple traits by a Single Gene. The word ‘Pleiotropy' is derived from a Greek word which means more ways. Father of genetics Gregor Johann Mendel made various interesting observations regarding the color of different plant components. Mendel then observed that the plants with colored seeds coats had colored flowers. He also observed that the pea plants had colorless seed coats with no pigmentation on their axils and white-colored flowers. The color of the seed coat had always been concerned with the specific axil and color of the flower. 

It is concluded that Mendel's observations were based on the result of Pleiotropy. Where an individual Gene plays it’s a role in multiple phenotypic traits.

Gene Pleiotropy

The gene pleiotropy is also referred to as 'Molecular Gene Pleiotropy. The gene which focuses on the number of functions of a particular gene is referred to as the gene Pleiotropy. Talking about Mendel’s experiment with white-colored flower and purple-colored plants, we do not think about phenotype concerned with the colors of two flowers. Mendel noticed that colors were always related to the two different colored seed coats and the color of the axil. A plant with white-colored flowers consists of brown-grey colored coats while plants bearing purple flowers have brown-grey colored seeds coats with reddish axils. Therefore instead of affecting only one characteristic, the color gene affects three characteristics.

Human Gene Disorders 

The genes affected by human genetic disorders are mostly pleiotropic genes. 

Examples of Pleiotropy

Example 1 

Phenylketonuria is a genetic disorder caused by the low metabolism of the amino acid phenylalanine in the body cells. This disorder is caused by the deficiency of an enzyme phenyl aniline hydroxylase, which is necessary to convert the essential amino acid phenyl aniline to tyrosine. Deficiency of enzyme aniline hydroxylase results in pain, lung disorder, eczema, etc.

Pleiotropic genes can provide valuable information about the evolution of different genes and gene families as genes are co-opted for new purposes. In other words, pleiotropy reflects the fact that most proteins have multiple roles in distinct cell types. Any genetic change which is responsible for the alteration in gene expression and its function can have wide-ranging effects in the variety of tissues.

Example 2 

Marfan syndrome is a disorder caused due to the defect in a single gene,  as it is responsible for affecting various growth factors.

Symptoms caused due to Marfan syndrome

  • Abnormal tall height.

  • Dislocation of the eye lens.

  • Lean fingers

  • Heart problems including the aorta, large blood vessels that carry blood away from the heart, ruptures.

The pleiotropic gene encodes a protein into chains and makes fibrils that provide flexibility and strength to the body’s connective tissues. In Marfan syndrome, it minimizes the amount of metabolism protein formed by the body and results in lesser fibrils. 

Frizzled feather trait is a disorder that occurs in chickens. Chickens with mutated gene display feathers that curl outward as opposed to lying flat. Another effect seen in chickens is faster metabolism and enlarged organs. The curling of features results in loss of the heat in the body which is required for a faster metabolism to maintain homeostasis. Other biological changes are higher food consumption, infertility, and delayed sexual maturation.

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Pleiotropy and Lethal alleles

Lethal alleles are alleles causing the death of organisms carrying them. These alleles are also referred to as lethal genes.  These alleles cause mutations in genes that are essential for growth or development. Depending on the number of genes involved lethal alleles may be recessive, dominant, or conditional. Death of organisms carrying lethal genes can happen any time after birth, though they manifest early in development. 

FAQ (Frequently Asked Questions)

1.What is the difference between pleiotropy and epistasis?

Pleiotropy refers to the involvement of one gene in many different phenotypes. This can be explained with an example of the CFTR  gene when the mutated gene causes cystic fibrosis. Cystic Fibrosis is a disease in which there is a perturbation of systems including the lungs, liver, pancreas, kidneys, and bowel.

Epistasis refers to the interaction of multiple genes (two or more loci) to determine a phenotype outcome.

Epistasis mostly occurs when two or more genes encoding proteins have a shared biochemical pathway. In Epistasis interactions, the genes are involved in a similar pathway, there may be competition for the same substrate.

2. What is sickle cell anemia?

Sickle cell anemia refers to a group of disorders that causes red blood cells to break down. This disease is caused by a mutation in the gene which helps our body to make the iron-rich compound hemoglobin d enables red blood cells to carry oxygen from the lungs throughout our body.

In this disease, an inherited group of disorders red blood cells contort into a sickle cell shape. Leaving a shortage of healthy red blood cells (sickle cell anemia), the cells die early. This can block the flow of the blood causing pain in the body.

Some symptoms of Sickle cell anemia are pain, infections, fatigue. Treatment includes medication, blood transfusion, and rarely a bone- marrow transplant.