Pleiotropy’s Role in Human Genetics and Exam Success
Pleiotropy is the process of having multiple traits because of a single gene. ‘Pleiotropy’ is a Greek word. Its meaning is having many or more ways. In this article, we will study the process and effects of Pleiotropy. Starting with Gene Pleiotropy to Human Gene Disorder. Let us start with understanding the meaning of Gene Pleiotropy.
Gene Pleiotropy is also known as Molecular Gene Pleiotropy. The gene which centres around the number of elements of a specific gene is alluded to as the gene Pleiotropy. Discussing Mendel’s test with white-shaded flowers and purple-hued plants, we do not contemplate aggregate worries about the shades of two flowers. Mendel saw that tones were constantly identified with the two distinctive shaded seed coats and the shade of the axil. A plant with white-hued flowers (also known as blossoms) comprises brown-dark-hued coats while plants bearing purple blossoms have brown-dim shaded seeds coats with ruddy axils. Along these lines as opposed to influencing just a single trademark, the shading gene influences three qualities.
Gene Disorders in Human Beings
The genes also affect human beings, which are known as human genetic disorders. Let us discuss a few genetic disorders with examples.
Illustration 1 -
There is a genetic disorder called Phenylketonuria. It is generally caused by the low metabolism rate of the amino acid (phenylalanine) in all the cells of the body. When there is a deficiency of an enzyme called the phenyl aniline hydroxylase enzyme. This enzyme is very important to convert amino acid phenyl aniline to tyrosine. This deficiency or this disorder results in lung disorder, pain, eczema, etc. Pleiotropic genes can give significant data about the advancement of various genes and gene families as genes are co-settled on new purposes. All in all, pleiotropy mirrors the way that most proteins play various parts in unmistakable cell types. Any genetic change which is answerable for the modification in gene articulation and its capacity can have wide-running impacts on the assortment of tissues.
Illustration 2 -
Another disease is known as Marfan syndrome. It is caused by a single gene. A single gene can be responsible for the growth of various body cells. The symptoms that are shown in this are dislocation of the eye lens, lean fingers, abnormal tall height, heart problems such as affecting the aorta, blood vessels, and so on. It works to minimize the metabolism of the body.
FAQs on What Is Pleiotropy? Explained with Gene Disorder Examples
1. What is pleiotropy as defined in Class 12 Biology?
In genetics, pleiotropy is the phenomenon where a single gene influences two or more seemingly unrelated phenotypic traits. Unlike the simple Mendelian concept of one gene controlling one characteristic, a pleiotropic gene can have multiple, diverse effects across the body. The underlying cause is often a single gene that codes for a protein with multiple functions or that is expressed in various cell types.
2. What are the three main examples of pleiotropy in human genetic disorders?
Three classic examples of pleiotropy in human diseases are:
- Phenylketonuria (PKU): Caused by a mutation in a single gene that codes for the enzyme phenylalanine hydroxylase. This leads to mental retardation, reduced hair, and skin pigmentation.
- Sickle-Cell Anaemia: A mutation in the gene for the beta-globin chain of haemoglobin causes multiple issues, including sickled red blood cells, anaemia, organ damage, and resistance to malaria.
- Marfan Syndrome: A defect in a single gene for a connective tissue protein results in a tall, lanky stature, lens dislocation in the eyes, and life-threatening aorta problems.
3. How does Phenylketonuria (PKU) demonstrate the effects of a pleiotropic gene?
Phenylketonuria is a prime example of pleiotropy because a single genetic defect has a cascade of consequences. The gene responsible codes for the enzyme phenylalanine hydroxylase. When this enzyme is non-functional, the amino acid phenylalanine accumulates in the body. This single metabolic block leads to multiple distinct phenotypes: it is converted into toxic derivatives that cause mental retardation, and it also interferes with the synthesis of melanin, leading to light skin and hair.
4. What is the key difference between pleiotropy and polygenic inheritance?
Pleiotropy and polygenic inheritance are opposite concepts. Pleiotropy is when one gene affects multiple traits (e.g., the gene for sickle-cell anaemia causing multiple health issues). In contrast, polygenic inheritance is when multiple genes collectively control one single trait (e.g., human skin colour or height, which are determined by the combined effect of several different genes).
5. How can the single gene mutation in sickle-cell anaemia lead to such a wide range of symptoms?
The single mutation in the HBB gene responsible for sickle-cell anaemia changes one amino acid in the haemoglobin protein. This altered protein causes red blood cells to deform into a sickle shape, especially under low oxygen conditions. This primary change leads to a wide range of secondary problems: the sickled cells are destroyed rapidly, causing anaemia and fatigue. They also clump together, blocking small blood vessels, which results in severe pain crises, tissue damage, and organ failure. This chain reaction from a single gene defect to a multi-system disorder is a classic illustration of pleiotropy.
6. What observation in pea plants first suggested the concept of pleiotropy?
Gregor Mendel himself observed a phenomenon that we now understand as pleiotropy. He noted that in pea plants, the gene that determined the flower colour (purple or white) also influenced two other traits: the colour of the seed coat (grey-brown or white) and the colour of the leaf axils (reddish or colourless). A single gene was controlling three distinct characteristics, providing an early example of pleiotropy in plants.
7. What is the molecular basis of pleiotropy?
The molecular basis of pleiotropy explains how one gene can have many effects. It usually happens in one of two ways:
- The gene codes for a protein that has multiple jobs in the body. For instance, a protein might function as both an enzyme in one pathway and a structural component in a different cell type.
- The gene's protein product is part of an interconnected biochemical pathway. A defect in one step can affect all subsequent steps, leading to diverse outcomes in different tissues.
Essentially, pleiotropy reflects the fact that most proteins do not operate in isolation but are part of a complex network of interactions within an organism.
