If I have type O blood, what do my parents have?
1 Answer
Either of your parents can have any blood type except AB as long as they are heterozygous for type A or B.
Explanation:
For your blood type to be O, you had to have inherited on O gene from each parent.
That means that either parent could be
AO (but not AA) -- blood type A
BO (but not BB) -- blood type B
OO -- blood type O
If either one of your parents had blood type AA, that parent would have automatically donated a gene for A blood to you, so your blood type could not be O.
The same is true if either one of your parents had blood genotype BB. You would automatically received one gene for type B, so your blood type could not be O.
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However, AA is not the only way to end up with type A blood, and BB is not the only genotype for type B blood.
A parent who is blood type A might have the genotype AO.
One half of the offspring of this parent will get a gene for type O.
A parent who has blood type B might have the genotype BO.
One half of this parent's offspring will get a gene for O.
A parent whose blood type is O has a genotype of OO, so all this parent's offspring will get a gene for O.
