Question

A child with blood group A has the father with blood group B and the mother with blood group AB. Choose the option that gives the correct genotypes of father, mother and the child :

• A. Father: I$^{\text{A}}$i, Mother: I$^{\text{B}}$i, Child: I$^{\text{A}}$i
• B. Father: I$^{\text{A}}$I$^{\text{B}}$, Mother: I$^{\text{A}}$i, Child: I$^{\text{A}}$I$^{\text{A}}$
• C. Father: I$^{\text{B}}$i, Mother: I$^{\text{A}}$I$^{\text{B}}$, Child: I$^{\text{A}}$i
• D. Father: I$^{\text{B}}$I$^{\text{B}}$, Mother: I$^{\text{A}}$I$^{\text{B}}$, Child: I$^{\text{A}}$I$^{\text{A}}$

Hint:

In ABO blood group inheritance, a child with blood group A must inherit at least one I$^{\text{A}}$ allele, which can come from a parent with blood group A or AB.

Answer 1

The Correct Option is C

Step 1: Blood group A in the child means the genotype is I$^{\text{A}}$I$^{\text{A}}$ or I$^{\text{A}}$i.
Step 2: The father has blood group B (genotype I$^{\text{B}}$I$^{\text{B}}$ or I$^{\text{B}}$i) and the mother has blood group AB (genotype I$^{\text{A}}$I$^{\text{B}}$).
Step 3: For the child to have blood group A, they must inherit I$^{\text{A}}$ from the mother (since the father cannot provide I$^{\text{A}}$) and either i or I$^{\text{B}}$ from the father. Since the child’s phenotype is A, the father must contribute i, making his genotype I$^{\text{B}}$i, and the child’s genotype I$^{\text{A}}$i.
Thus, the correct genotypes are Father: I$^{\text{B}}$i, Mother: I$^{\text{A}}$I$^{\text{B}}$, Child: I$^{\text{A}}$i.