Pleiotropy: Definition & Examples

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  • 0:00 Overview of Genetics
  • 0:35 What Is Pleiotropy?
  • 1:40 Examples
  • 3:04 Lesson Summary
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Lesson Transcript
Instructor: Jeremy Battista

Jeremy has a master of science degree in education.

There are many different mutations that occur during growth in organisms. Many times, these mutations can be passed on and will occur in such a way as to be beneficial to the organism. Sometimes, they are not. We will be looking at one such type of mutation here.

Overview of Genetics

In genetics, we look at how traits are inherited or passed on from generation to generation. We find that the genotype of an organism will tell you what their genes and DNA look like. The phenotype will be how those genes are expressed or what they were coded for. For example, your genotype for having brown eyes might be BB, and your phenotype will be your actual brown eyes.

This is just a very simple example, as genetics can get pretty complex. Remember, though, the genotype refers to what your genes are. Your phenotype refers to what is expressed because of those genes.

What Is Pleiotropy?

Occasionally, we see genetic mutations in human beings. A mutation is any sort of genetic alteration that causes a change in the phenotype or expression of that gene. Sometimes we see genetic changes and phenotype changes not from a mutation, but from a gene controlling multiple traits. This is called pleiotropy. As stated, pleiotropy is where one gene winds up controlling multiple phenotypic traits in the organism.

Pleiotropy can be found in many different forms, but mainly it is viewed as causing inherited diseases and disorders. What can also occur is that if that gene has a mutation, it ultimately affects all of the phenotype traits that the gene was controlling. This creates a trickle-down effect. As the gene gets mutated, so do the traits it would exhibit.

There is a specific type of pleiotropy called antagonistic pleiotropy, where some of the traits that are expressed end up being beneficial to the organism but the others end up being detrimental. The organism will benefit from one of the expressions, but another might harm the organism.


When researching pleiotropy, we see a number of examples come up time and time again. One such example is phenylketonuria, or PKU for short. PKU affects the body's ability to break down phenylalanine (an amino acid) into tyrosine (another amino acid). The phenylalanine just sits there, building up more and more until eventually damage is done to the person.

This most often is only a real issue in infants and young children. Restricting their intake of phenylalanine will oftentimes resolve any issue. If left unchecked, however, this can result in mental retardation of the child.

Sickle cell anemia is another pleiotropic disease found in humans. A normal blood cell looks similar to a life raft on a boat. In the case of those with sickle cell anemia, we see the blood cell altered to form a crescent shape instead. This leads to blockages and increased risk of heart attacks and strokes.

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