blood types an example of a trait controlled by multiple alleles

Blood typesAn example of a trait controlled by multiple alleles

ABO blood types

There are four basic blood types, in order from most common to least common they are: O, A, B, and AB. Blood type is determined by the "alleles" that we inherit from our parents. Alleles are possible types of a particular gene, in this case the blood type gene. There are three basic blood type alleles: A, B, and O. We all have two alleles, one inherited from each parent. The possible combinations of the three alleles are:

OO AO BO AB AA BB

Codominance

Blood types A and B are called "codominant" alleles, while O is "recessive." A codominant allele is apparent even if only one is present; a recessive allele is apparent only if two recessive alleles are present. Since blood type O is recessive, it is not apparent if the person inherits an A or B allele along with it.

So, the possible allele combinations result in a particular blood type in this way:

Genotype: OO Phenotype: blood type O

Genotype: AO Phenotype: blood type A

Genotype: BO Phenotype: blood type B

Genotype: AB Phenotype: blood type AB

Genotype: AA Phenotype: blood type A

Genotype: BB Phenotype: blood type B

Antigens and antibodies

Antigens and antibodies

ABOBlood Type

Antigen A

Antigen B

Anti-A antibody

Anti-B antibody

A Yes No No Yes

B No Yes Yes No

AB Yes Yes No No

O No No Yes yes

Rh factor

Rhesus (Rh) factor is an inherited trait that refers to a specific protein found on the surface of red blood cells. If your blood has the protein, you're Rh+ (85% of the population). If your blood lacks the protein, you are Rh negative.

Rh factor and pregnancy

What May Happen If I Am Rh-Negative And Pregnant?

If you are Rh-negative, you may develop antibodies to an Rh+ baby. If a small amount of the baby’s blood mixes with your blood, which often happens, your body may respond as if it were allergic to the baby. Your body may make antibodies to the Rh antigens in the baby’s blood. This means you have become sensitized and your antibodies can cross the placenta and attack your baby’s blood.

How can problems be prevented?

A blood test can provide you with your blood type and Rh factor.

Antibody screen is another blood test that can show if an Rh-negative woman has developed antibodies to Rh-positive blood.

An injection or Rh immunoglobulin (RhIg), a blood product that can prevent sensitization of an Rh-negative mother.

RhIg is used during pregnancy and after delivery

If a woman with Rh-negative blood has not been sensitized, her doctor may suggest that she receive RhIg around the 28th week of pregnancy to prevent sensitization for the rest of pregnancy.

If the baby is born with Rh+ blood, the mother should be given another dose of RhIg to prevent her from making antibodies to the Rh+ cells she may have received from their baby before and during delivery.

The treatment of RhIg is only good for the pregnancy in which it is given. Each pregnancy and delivery of an Rh+ child requires repeat doses of RhIg.

Blood transfusions

In a blood transfusion, a patient must receive a blood type compatible with his or her own blood type. If the blood types are not compatible, red blood cells will clump together, making clots that can block blood vessels and cause death. It is important that blood types be matched before blood transfusions take place. In an emergency, type O blood can be given because it is most likely to be accepted by all blood types.

Percentages of blood types in the population

  Caucasians African American

Hispanic Asian

O + 37% 47% 53% 39%

O - 8% 4% 4% 1%

A + 33% 24% 29% 27%

A - 7% 2% 2% 0.5%

B + 9% 18% 9% 25%

B - 2% 1% 1% 0.4%

AB + 3% 4% 2% 7%

AB - 1% 0.3% 0.2% 0.1%

Who can donate? Who can receive?

Blood Type Donate Blood To

Receive Blood From

A+ A+ AB+ A+ A- O+ O-

O+ O+ A+ B+ AB+

O+ O-

B+ B+ AB+ B+ B- O+ O-

AB+ AB+ Everyone

A- A+ A- AB+ AB-

A- O-

O- Everyone O-

B- B+ B- AB+ AB-

B- O-

AB- AB+ AB- AB- A- B- O-

Universal donor:Type O

Universal recipient:Type AB

Parents' Blood Types

Possible Children

Impossible Children

A & A A, O B, ABA & B A, B, AB, O noneA & AB A, B, AB OA & O A, O B, ABB & B B, O A, ABB & AB A, B, AB OB & O B, O A, ABAB & AB A, B, AB OAB & O A, B AB, OO & O O A, B, AB