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Blood Type Inheritance in Humans

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  • 0:03 Human Blood Types
  • 1:17 Blood Type Inheritance
  • 3:28 Punnett Squares
  • 5:01 Lesson Summary
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Lesson Transcript
Instructor: Stephanie Matalone

Stephanie taught high school science and math and has a Master's Degree in Secondary Education.

This lesson explains differences among the four blood types in humans: A, B, AB, and O. It also shows how these blood types are passed from parents to children.

Human Blood Types

If you've donated blood before, you were probably told what blood type you have: A, B, AB, or O. But why is this important? Your blood can't be given to another person without first identifying the type because red blood cells have different antigens based on blood type.

Antigens are structures that cause an immune response in the body. This means that if you donate blood to someone whose blood has different antigens than yours, his or her immune system will produce antibodies aimed at destroying the donated blood.

A person with blood type A has red blood cells with A antigens, while a person with blood type B has red blood cells with B antigens. Someone with the AB blood type has both A and B antigens, while someone with O blood type has no antigens. This is why a person who has an O blood type is called a universal donor. The lack of antigens means that people with blood types A, B, and AB can receive O blood without having an immune response.

Blood Type Inheritance

So, what determines blood type? Blood type is inherited based on the transfer of alleles from parents to offspring. Alleles are different forms of genes, which are pieces of DNA that carry genetic information. Blood type alleles are formally depicted with the letter 'I' or 'i,' but can be simplified by using the blood type letter.

Blood type inheritance is more complicated than typical Mendelian inheritance, where there are only two alleles: one dominant and one recessive. Dominant alleles mask recessive alleles when a person receives both.

Of the three possible blood type alleles (A, B, and O), each person receives two - one from each parent - which determines their blood type. These two alleles together are the genotype, or genetic makeup. This genotype determines the blood type, which is a phenotype, or physical characteristic.

A person with type A blood can have two possible genotypes: AA or AO. A person with B blood type also can have two genotypes: BB or BO. The A and B alleles are dominant over the O allele, which means the O allele is recessive and will be masked.

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