Question

I have type O blood. My dad has type O blood. My mother has type A blood. How is this possible?

What is my, my dad's, and my mother's genotype for blood type? What are the possible blood types of my siblings? Is blood type and example of "incomplete dominance" or, "codominance"?

Answer 1

ABO blood types can be complicated to understand. This is mostly due to the fact that the 'O-type' antigen is masked by the presence of an A- or B-type antigen. This is explained in the following chart, showing the different the genotypes that make up the blood types.

Genotype (DNA)	Blood Type
AO or AA	A blood type
AB	AB blood type
BO or BB	B blood type
OO	O blood type

For example, two O blood type parents can produce a child with only O blood type. Two parents with A blood type can produce a child with either A or O blood types. Two parents with B blood type can produce a child with either B or O blood type. One parent with A and another with B can produce a child with A, B, AB or O blood types. If one parent has A and another has AB, they can either produce a child with A, B or AB blood types. If one parent has A and another has O, they can either produce a child with A or O blood types.

Mother's Blood Type	Possible Mother's Genotype	Father's Blood Type	Possible Father's Genotype	Possible Child Blood Type
A	AA, AO	A	AA, AO	A, O
A	AA, AO	AB	AB	A, AB, B
A	AA, AO	B	BB, BO	A, AB, B, O
A	AA, AO	O	OO	A, O