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Polygenic Traits and Pleiotropy

Polygenic Traits and Pleiotropy

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This lesson will explain what a polygenic trait is and give examples of polygenic and pleiotropy traits.

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Tutorial

What's Covered

This lesson will cover how different traits can be expressed by covering:

  1. Polygenic Traits
  2. Penetrance
  3. Pleiotropy

1. Polygenic Traits

Polygenic traits are traits the combined expressions of multiple genes. In other words, these traits are not determined by just one single gene. Most of the traits that are expressed are actually determined by many genes, with very few traits determined by one single gene.

ExampleThe color of your eyes, hair, or skin are all polygenic traits

Term to Know

    • Polygenic Trait
    • A trait that is determined by several genes.

Polygenic traits can show continuous variation within a population. Height is a good example of a polygenic trait because, within a given population, we could have a wide range of continuous differences of that trait. Height is also a multifactorial trait, meaning that it is determined by multiple factors such as the combination of a person’s genes and environment.

ExampleNutrition is an example of an environmental factor that can influence height.

Terms to Know

    • Continuous Variation
    • Variation of a trait that shows up in a population of people, body height for instance.
    • Multifactorial Trait
    • A gene that is partially controlled by genetics and partially controlled by the environment. For example, body height is genetic but nutrition growing up also influences height.

2. Penetrance

Penetrance is the varying degree to which someone expresses a trait that's associated with an allele. This means that some people with inherited alleles for trait might have varying phenotypes. A trait can have incomplete penetrance and can be completely penetrant.

Term to Know

    • Penetrance
    • The degree to which an inherited allele is expressed in the phenotype. An example would be achondroplastic dwarfism; if a person inherits the allele and it presents, they will be a dwarf.

Cystic fibrosis is an example of a trait that would be completely penetrate. This means that 100% of people who are homozygous recessive will have cystic fibrosis.

Polydactyly would be an example of a trait that would be incompletely penetrant. Polydactyly relates to the number of digits that a person has. Some people who carry the genes for polydactyly might have the normal 10 fingers, while some people who have that trait might have more than 10 fingers. There are varying degrees to which someone expresses this trait.


3. Pleiotropy

Pleiotropy is the expression of one gene that affects multiple traits. An example of this is the gene that causes sickle-cell anemia. This gene produces various affects throughout the body and can affect the way the blood carries oxygen, other internal organs, et cetera.

Terms to Know

    • Pleiotropy
    • When one gene influences multiple phenotypic traits. Examples would be sickle-cell anemia and phenylketonuria (PKU).
    • Sickle-cell Anemia
    • An example of pleiotropy, a person who inherits the mutated HBs gene will contract sickle-cell anemia which damages erythrocytes, the spleen and many other organs of the body.

Summary

Polygenic traits are a combined expression of multiple genes. Examples would be the color of your eyes, hair, of skin. These traits can show continuous variation in a population, and can also be multifactorial. Penetrance is the varying degree to which a trait associated with an allele is expressed. Pleiotropy is the expression of multiple traits from one gene such is the case with the gene for sickle-cell anemia.

Keep up the learning and have a great day!

Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Polygenic Trait

    A trait that is determined by several genes.

  • Continuous Variation

    Variation of a trait that shows up in a population of people, body height for instance.

  • Multifactorial Trait

    A gene that is partially controlled by genetics and partially controlled by the environment. For example, body height is genetic but nutrition growing up also influences height.

  • Penetrance

    The degree to which an inherited allele is expressed in the phenotype. An example would be achondroplastic dwarfism; if a person inherits the allele and it presents, they will be a dwarf.

  • Pleiotropy

    When one gene influences multiple phenotypic traits. Examples would be sickle-cell anemia and phenylketonuria (PKU).

  • Sickle-cell Anemia

    An example of pleiotropy, a person who inherits the mutated HBs gene will contract sickle-cell anemia which damages erythrocytes, the spleen and many other organs of the body.