NEET 2024 Zoology Question 199 Solution

ABO blood groups are controlled by the gene $I$, which has three alleles: $I^A$, $I^B$, and $i$. The alleles $I^A$ and $I^B$ are codominant with each other and both are completely dominant over the recessive allele $i$.

A person with blood group O exhibits the phenotype of the recessive allele and must have the homozygous genotype: $$\text{Child} = ii$$

For the child to receive one $i$ allele from the father and one $i$ allele from the mother, both parents must possess at least one $i$ allele: - Father (Blood group B): Can be $I^B I^B$ or $I^B i$. Since he must donate $i$, his genotype is $I^B i$. - Mother (Blood group A): Can be $I^A I^A$ or $I^A i$. Since she must donate $i$, her genotype is $I^A i$. Respective genotypes (Father / Mother / Child): $$I^B i \;/\; I^A i \;/\; ii$$

Only Statement A correctly represents $I^B i \;/\; I^A i \;/\; ii$. Thus, the answer is "A only", corresponding to Option (3).