ABO Blood Groups

The gene for blood type, gene l, codes for a molecule that attaches to a membrane protein found on the surface of red blood cells. The ABO Blood Group The l A and l B alleles each code for a different molecule. Your immune system recognizes the red blood cells as belonging to you. If cells with a different surface molecule enter your body, your immune system will attack them

Blood Types Blood is named for the antigen present on the red blood cell Antigens are substances that stimulate an immune response in the body. The letters A and B stand for the types of blood surface antigens found on human red blood cells.

The l A allele is dominant to i, so inheriting either the l A i alleles or the l A l A alleles from both parents will give you type A blood. Phenotype A Surface molecule A is produced. Surface molecule A

The l B allele is also dominant to i. Phenotype B To have type B blood, you must inherit the l B allele from one parent and either another l B allele or the i allele from the other. Surface molecule B is produced. Surface molecule B

The l A and l B alleles are codominant. Phenotype AB This means that if you inherit the l A allele from one parent and the l B allele from the other, your red blood cells will produce both surface molecules and you will have type AB blood. Surface molecule B Surface molecule A

The i allele is recessive and produces no surface molecules. Phenotype O Therefore, if you are homozygous ii, your blood cells have no surface molecules and you have blood type O.

Multiple Alleles Govern Blood Type Human Blood Types l A l A or l A i l B l B or l B i lA lBlA lB ii Genotypes Surface MoleculesPhenotypes A B A and B None A B AB O

Blood surface antigens determine blood group Blood plasma contains proteins, called antibodies, that are shaped to correspond with the different blood surface antigens.

Antigens react with antibodies of the same name The antibody in the blood plasma reacts with its matching antigen on red blood cells if they are brought into contact with one another. This reaction results in clumped blood cells that can no longer function. For example, if you have type A blood, you have the A antigen on your red blood cells and the anti-B antibody in your plasma.

If you had anti-A antibodies, they would react with your own type A red blood cells. Clumped blood cells cannot carry oxygen or nutrients to body cells.

Blood produces antibodies for antigens its does not have. Example: A blood type produces B antibodies – because it does not have B antigens on its red blood cells.