Genotypes for Various Blood Types

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  • 0:03 What Are Blood Types?
  • 0:57 Genotypes
  • 2:50 Lesson Summary
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Lesson Transcript
Instructor: Dominic Corsini
What are the primary human blood types and how is each determined? This lesson helps answer those questions through an investigation into genotypes and their relationship to blood type.

What Are Blood Types?

When you look in the mirror certain traits are apparent. The color of your eyes, the shape of your chin, and the dimples on your cheeks are evident to even the casual observer. However, other characteristics are a little more hidden. For example, do you know your blood type? Blood types are categories of blood classified by the presence or absence of antigens on the surface of red blood cells. Antigens are structures that extend off the red blood cell. Type A blood contains one type of antigen, while type B blood contains a different type. Type AB blood contains antigens from both A and B, while type O blood contains no antigens.

Blood Antigens
Blood Antigens

Humans possess four basic blood types: A, B, AB, and O. Blood type is not overtly noticeable and must be learned via a blood test. For this reason, many people are unaware of their blood type.


Blood type is determined by our genes. Genes are segments of DNA that code for specific traits. Different versions of genes are called alleles. When determining something such as blood type, individuals receive one allele from their biological mother and another allele from their biological father. It's the combination of these alleles that creates the gene for blood type. This combination of alleles is called a genotype. Now let's relate this genotype (allele combination) to blood types.

Blood type alleles are an interesting mix, so to better understand them, let's provide some background information. The allele for type A blood is a dominant allele. In other words, when someone receives this allele from a parent, he or she will exhibit the type A antigen. The same is true of the type B allele: if someone receives the type B allele from a parent, he or she will have the type B antigen. The type O allele is recessive, meaning it will be hidden or masked by the A or B alleles.

So what does all this mean with respect to actual blood types?

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