Codominance: Definition & Example

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  • 0:00 Definition of Codominance
  • 0:45 Examples of Codominance
  • 2:20 Lesson Summary
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Lesson Transcript
Instructor: Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

There are numerous factors that play a role in determining how an organism will look and act. In this lesson, you will learn about a genetic situation known as codominance.

Definition of Codominance

We look and act the way we do because of our genes. Genes are units of hereditary information that are located on segments of chromosomes. The genes for a specific trait may exist in different forms known as alleles.

An example of an allele or a gene is a flower color. A flower may have alleles that make it red, or pink, and so on. Alleles that always show up when they are present are known as dominant alleles. Alleles that are masked or hidden by dominant alleles are known as recessive alleles. In some situations, both alleles are expressed equally. A genetic scenario where neither allele is dominant or recessive and both get expressed is known as codominance.

Examples of Codominance

Do you know your blood type? Blood types are excellent examples of codominance. A person's blood type can be A, B, AB, or O. The letters refer to the types of proteins present in the blood.

If a person has the type A protein, they have type A blood. If a person has the type B protein, they have type B blood. If a person has type O blood, then neither protein is present. If a person is type AB, then they have both A and B proteins present in their blood. If a person is type A or type B, this means that they have the dominant A or dominant B allele present in their blood. All other alleles are masked. If a person is type O, it means that neither the type A or type B allele is dominant. However, if a person is type AB, this means that both the A allele and the B allele are equally expressed and are therefore codominant.

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