Human blood groups are determined by the ABO gene, which has three alleles: \( I^A \), \( I^B \), and \( i \). The \( I^A \) and \( I^B \) alleles are codominant, while \( i \) is recessive. The genotypes for the blood groups are: - Blood group AB: \( I^A I^B \) - Blood group O: \( ii \) A man with blood group AB has the genotype \( I^A I^B \), and a woman with blood group O has the genotype \( ii \). To determine the probability of their child having blood group A, a Punnett square is used to show the possible genotypes of their offspring. The man (\( I^A I^B \)) can pass on either an \( I^A \) or an \( I^B \) allele. The woman (\( ii \)) can only pass on an \( i \) allele. The possible offspring genotypes are: \[ \begin{array}{c|cc} & I^A & I^B
\hline i & I^A i & I^B i
\end{array} \] - \( I^A i \): Results in Blood group A (as \( I^A \) is dominant over \( i \)). - \( I^B i \): Results in Blood group B (as \( I^B \) is dominant over \( i \)). The possible blood groups for the offspring are: - Blood group A (\( I^A i \)): 1 out of 2 possibilities. - Blood group B (\( I^B i \)): 1 out of 2 possibilities. Therefore, the probability that their child will have blood group A is: \[ \frac{1}{2} = 50\% \]