Blood Types – ABO

The Human ABO markers: The A, B, and O alleles

 *** March is American Red Cross Month ***

Human blood type is determined by co-dominant alleles. An allele is one of several different forms of genetic information that is present in our DNA at a specific location on a specific chromosome.

Blood Types

There are three different alleles for human blood type:

Blood types For simplicity, we call these IA A IB B i O

 Genotypes

Each of us has two ABO blood type alleles, because we each inherit one blood type allele from our biological mother and one from our biological father. A description of the pair of alleles in our DNA is called the genotype. Since there are three different alleles, there are a total of six different genotypes at the human ABO genetic locus.

Allele from Parent 1 Allele from Parent 2 Genotype of offspring Blood types of offspring A A AA A A B AB* AB A O AO A B A AB* AB B B BB B B O BO B O O OO O

How are blood types related to the six genotypes?

A blood test is used to determine whether the A and/or B characteristics are present in a blood sample. It is not possible to determine the exact genotype from a blood test result of either type A or type B.

If someone has blood type A, they must have at least one copy of the A allele, but they could have two copies. Their genotype is either AA or AO. Similarly, someone who is blood type B could have a genotype of either BB or BO.

Blood type Possible genotypes A AA AO B BB BO

A blood test of either type AB or type O is more informative. Someone with blood type AB must have both the A and B alleles. The genotype must be AB. Someone with blood type O has neither the A nor the B allele. The genotype must be OO.

Blood type Possible genotypes AB AB O OO

How are ABO alleles inherited by our children?

Each biological parent donates one of their two ABO alleles to their child. A mother who is blood type O can only pass an O allele to her son or daughter. A father who is blood type AB could pass either an A or a B allele to his son or daughter. This couple could have children of either blood type A (O from mother and A from father) or blood type B (O from mother and B from father).

 

Inherited	Blood type of child
O from the mother A from the father	A
O from the mother B from the father	B

 

Since there are 4 different maternal blood types and 4 different paternal blood types possible, there are 16 different combinations to consider when predicting the blood type of children.

For a blood type calculator visit http://www.biology.arizona.edu/Human_Bio/problem_sets/blood_types/inherited.html

Exterpts from http://www.biology.arizona.edu/Human_Bio/problem_sets/blood_types/Intro.html

The Red Cross

• Almost 40% of the population has O+ blood
   
• Patients with Type O blood must receive Type O blood
   
• About half of all blood ordered by hospitals in our area is Type O
   
• Type O blood is the universal blood type and is the only blood type that can be transfused to patients with other blood types
   
• Only about 7% of all people have Type O negative blood
   
• Type O negative blood is the preferred type for accident victims and babies needing exchange transfusions
   
• There is always a need for Type O donors because their blood may be transfused to a person of any blood type in an emergency

If your blood type is . . .