The ABO blood group system consists of four different blood groups, which describe whether an individual’s red blood cells carry the A antigen, B antigen, both, or neither. The ABO gene has three alleles: ^IA, ^IB, and i. The i allele is recessive to both IA and IB, while the ^IA and ^IB allels are codominant. Individuals homozygous for the i allele are known as blood group O, with neither A nor B antigens.

Blood group follows the rules of Mendelian single-gene inheritance – alleles are inherited independently from either parent, with probability 0.5.

(a) Suppose that both members of a couple have Group AB blood. What is the probability that a child of this couple will have Group A blood?

(b) Suppose that one member of a couple is genotype ^IBi and the other is ^IAi. What is the probability that their first child has Type O blood and the next two do not?

(c) Suppose that one member of a couple is genotype ^IBi and the other is ^IAi. Given that one child has Type O blood and two do not, what is the probability of the first child having Type O blood?

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Alleles inherited Blood type IA and IA A IA and IB AB IA and i IB and IB A B IB and i i and i B