Question Video: Predicting the Results of an Agglutination Test with Type A Blood and Anti-A Antibodies | Nagwa Question Video: Predicting the Results of an Agglutination Test with Type A Blood and Anti-A Antibodies | Nagwa

# Question Video: Predicting the Results of an Agglutination Test with Type A Blood and Anti-A Antibodies Biology • First Year of Secondary School

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The method for determining a person’s blood type by agglutination is outlined below: 1. A sample of blood is taken from the person who needs their blood type determined. 2. Two large drops of blood are placed on clean, sterile glass slides. 3. Anti-A antibodies are mixed in with one of the two drops of blood. 4. Anti-B antibodies are mixed in with the other drop of blood. What result (agglutination or no agglutination) would you expect for type A blood mixed with anti-A antibodies?

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### Video Transcript

The method for determining a person’s blood type by agglutination is outlined below. One, a sample of blood is taken from the person who needs their blood type determined. Two, two large drops of blood are placed on clean, sterile glass slides. Three, anti-A antibodies are mixed in with one of the two drops of blood. Four, anti-B antibodies are mixed in with the other drop of blood. What result, agglutination or no agglutination, would you expect for type A blood mixed with anti-A antibodies?

This question provides us with a method of determining someone’s blood type and asks us to predict the result when blood type A is mixed with anti-A antibodies. To answer it, first, let’s look at the four different blood types: A, B, AB, and O. The four blood types are an example of a trait in humans that is controlled by a person’s genetics. There are three alleles, or alternative versions of genes, that can combine to make up those blood types. There are A, B, and O alleles that control blood type, written with a superscript over an I as shown in the second column of this table.

If a person has two IA alleles or an IA allele and an IO allele, they have blood type A. If a person has two IB alleles or an IB allele and an IO allele, they have blood type B. If a person has an IA and an IB allele, they have the AB blood type. Finally, if a person has two IO alleles, they have the O blood type.

So, what does this mean? Well, the IA allele codes for the production of type A antigens, which are proteins that can cause an immune response and are presented on the surface of cells, in this case red blood cells. Similarly, the IB allele codes for type B antigens. The IO allele doesn’t code for any antigen. Therefore, A and AB blood types have A antigens. B and AB blood types have B antigens. And the O blood type has none.

Antibodies are proteins that are produced by the body’s immune system in response to the presence of foreign antigens, thus helping to fight potentially dangerous substances in your body. Blood may contain anti-A antibodies, anti-B antibodies, both, or neither. Anti-A and anti-B antibodies can respond to and attack A and B antigens, respectively.

Let’s go over an example. If someone has blood type A, they would not produce anti-A antibodies because the type A antigen is not a foreign substance to their body. If they did, they would be in serious trouble because anti-A antibodies cause cells presenting type A antigens to agglutinate, or clump together.

When an antigen is mixed with a complementary antibody, they bind together. As antibodies have two binding sites, they can bind together two red blood cells. Agglutination occurs as more and more red blood cells are bound together in a clump.

On the other hand, someone with blood type A would usually naturally produce anti-B antibodies. As antibodies are highly specific to an antigen, anti-B antibodies cannot bind to type A antigens, so no agglutination would occur. Now we know what response we would expect if type A blood, which has A antigens, was mixed with anti-A antibodies. As anti-A antibodies agglutinate in the presence of type A antigens, the correct answer is agglutination.

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