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Inherited Disorders and Birth Defects

Blood type

02/19/2008

Question:

My question is if my blood type is O what other blood type would mix with mind to make my daughter blood type be B-? Because who I thought was her father is O as well so that tells me that he is not her father.

Answer:

In general, you are correct, if both parents have blood type O then any child they have should also have blood type O.

ABO blood types are inherited. A person’s blood type is determined by the inheriting 1 of 3 different forms of a gene (called alleles) from each parent - in this case - A, B, or O.

If both parents have A alleles - then the child will have AA genotype and have A blood group.

If both parents have B alleles - then the child will have BB genotype and have B blood group.

If both parents have O alleles - then the child will have OO genotype and have O blood group.

If one parent has A and one parent has B - then the child will have AB genotype and have AB blood group.

If one parent has A and one has O - then the child will have AO genotype and have A blood group.

If one parent has B and one has O - then the child will have BO genotype and have B blood group.

Both A and B forms of the gene are dominant over O. This means that if a person has AO or BO alleles, they will have A blood type or B blood type. People who have type O have an OO genotype - so they would not have children with either A blood type or B blood type.

You would expect that if you are O blood type (which means you have a OO genotype) and your daughter has B blood type (which means she has a BO genotype) then her father would also need to have B blood type (could be either BB or BO genotype).

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Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University