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Hello there Sir or Miss,
At school I am doing genetics of AP Biology and I have a test on it (SAC). I live in the Victorian state of Australia. I am having difficulty in understanding what the answer of this question is-

The ABO blood group system of humans is an autosomal trait that has three alleles as follows.
IA- protein A on red blood cells
IB- protein B on red blood cells
i- no protein on blood cell

In this system, four different blood groups exist. They are A,B,AB and O. In a family of four children, each children has a different blood group with respect to this gene. The phenotypes of the parent must be-

A)AB and O
B)A and B
C)B and AB
D)O and B

In my opinion I think the answer is A but it is an educated guess. In your opinion, what do you think the answer of this question is and why?
I will be much appreciated if you reply me with your answer.
Yours sincerely,
G.J

Hello G.J. (Draco),

Thank you for being upfront that your question is related to your exam!

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