Question

The probability of having a girl child with blood group O when the parents have blood group A and B is

• A. 0%
• B. At least 50%
• C. At most 25%
• D. Exactly 75%

Answer 1

Answer: (C)

At most 25%

Human blood group is governed by single gene "I" which has three alleles “I${}^A$", “I${}^B$” and “I${}^O$”. Genotype of a parent with “A” blood group can be I${}^A$I${}^O$ or I${}^A$I${}^A$ and that of parent with “B” blood group is I${}^B$I${}^B$ and I${}^B$I${}^O$. The alleles I${}^A$, I${}^O$ and I${}^B$ can make total six genotypic combinations, namely I${}^A$ I${}^A$, I${}^A$ I${}^O$, I${}^B$ I${}^B$, I${}^B$ I${}^O$, I${}^A$ I${}^B$ and I${}^O$I${}^O$. Thus, the possible blood group of their children are A, B, O and AB. Therefore, probability of having a girl child with blood group O is ¼ or 25%, as depending on the genotype of parents, there is equal probability of their child to have any of four blood groups.

Thus, the correct answer is option C.