Pleiotropy: Definition, Pleotropic Genes & Examples

Pleiotropy is a condition in which one single gene starts affecting multiple traits of living organisms and the genes responsible for pleiotropy are called pleotropic genes. The word pleiotropy is derived from two Greek words pleio, meaning "many," and tropic, meaning "affecting." It is important to study pleiotropic genes as it helps us understand the link between the traits and genetic disorders. Some common examples of pleiotropy are phenylketonuria and sickle cell anemia.

Pleiotropy 

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What is Pleiotropy?

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When a single gene controls the expression of multiple traits (eye color, height, body shape, etc.) the condition is called pleiotropy and is mainly caused by variations in genes. 

• While studying inheritance, some observations were made by Gregor Mendel related to several plant components.
• He observed that the plants that had colored seed coats also had colored leaf axils (a portion of the leaf that connects to the stem) and flowers.
• Another observation made by Mendel was that the pea plants had colorless seedcoats with white flowers.
• This shows that observations made by Gregor Mendel were a result of pleiotropy. 
• The gene responsible for the seedcoat color was also responsible for the color of the flower.

Gene Pleiotropy

Gene pleiotropy also called molecular-gene pleiotropy focuses on the number of roles of a specific gene. Mendel concluded that the colors were linked to two different characteristics: the color of the seed coat and axils.

• A plant having white-colored flowers contains colorless seed coats and axils whereas, brownish-grey color seed coats with red color axils were found in plants with purple flowers.
• As a result, the color gene affects three attributes rather than just one.

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Examples of Pleiotropy

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Following are some of the important examples of pleiotropy which are discussed below in detail:

Sickle-cell anemia

Sickle Cell Anemia is an inherited disorder caused by a genetic mutation. This results in abnormal shaped red blood cells which resemble a sickle. When a change in beta-globulin takes place, sickle cell anemia occurs. Due to this change, the normal blood flow is restricted which ultimately damages the heart, lungs, and other organs of the body. 

Phenylketonuria

Phenylketonuria, also called PKU is a disorder that is caused by the accumulation of the amino acid phenylalanine in the body. A change in the phenylalanine hydroxylase gene causes this disorder.

• This gene creates an enzyme that helps in the breakdown of phenylalanine.
• If this enzyme is not present excess accumulation of phenylalanine takes place causing serious health problems.

Marfan Syndrome

Marfan syndrome is one of the examples of pleiotropy, it is a type of genetic disorder in humans that impacts the connective tissues. Marfan Syndrome most commonly affects the heart, blood vessels, eyes, and skeleton.

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Things to Remember

• Marfan Syndrome, which affects the eyes, heart, skeleton, and blood vessels is an example of pleiotropy.
• The phenomenon that focuses on gene mutations and their effect on multiple traits is called developmental pleiotropy.
• Cystic fibrosis is also an example of such a phenomenon which affects the digestive system along with other organs.
• Gregor Mendel observed two characteristics: the color of seed coat and axils.
• The gene responsible for the development of wings in Drosophila is the vestigial gene. 

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Previous Years Questions

1.  Which of the following is an example of pleiotropy ?…..[ CUCET 2011]
2. Who proposed the chromosomal theory of inheritance ?….[CUCET 2010]
3. The children of a father with type 'O' blood and mother….[COMEDK UGET 2012]
4. Epicanthus skin fold above the eyes and transverse palmer….[COMEDK UGET 2007]
5. Distance between the genes and percentage of….[COMEDK UGET 2015]
6. Which one of the following is a sex-linked disease….​[CUCET 2010]
7. The science that deals with the application of principles….[CUCET 2010]
8. A 10 years old patient is found to have the following….[COMEDK UGET 2012]
9. Which of the following genes shows the heterozygous...[BHU UET 2008]
10. Which chromosomal constitution refers to Jacob's syndrome….[BHU UET 2012]
11. Mutations are caused due to...[JIPMER 2001]
12. 2n- 1 condition is called… [JIPMER 2003]
13. Which of the following chromosomes are responsible for..[UPSEEE 2016]
14. In order to lessen the suffering of phenylketonurics...[AMUEEE 2014]
15. In Mendel's experiments with garden pea, round seed shape..[JKCET 2015]
16. Genotypic and phenotypic ratio in monohybrid cross remains..[JKCET 2011]
17. The gene T that controls ABO blood groups….[NEET 2020]
18. One of the parents of a cross has mutation...[NEET 2004