Read the given passage and answer the question.

ABO blood groups in human beings are controlled by the gene $I$. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene ($I$) has three alleles $I^A, I^B$ and $i$. The alleles $I^A$ and $I^B$ produce a slightly different form of the sugar while allele $i$ does not produce any sugar. Because humans are diploid organisms, each person possesses any two of the three $I$ gene alleles. $I^A$ and $I^B$ are completely dominant over $i$.

The genotype of Universal donor is:

$ii$

The correct answer is Option (3) → $ii$

Individuals with blood type O are known as universal donors because their red blood cells lack A and B antigens, making their blood compatible with all other blood types in transfusions. The genotype for blood type O is ii, where both alleles are the recessive i alleles, leading to the absence of A or B antigens.

Here’s a breakdown of the other options:

• I^Ai: This genotype corresponds to blood type A.
• I^B: This is incomplete, but with an additional i or I^B allele, it would indicate blood type B.
• I^AI^B: This genotype corresponds to blood type AB, which is the universal recipient but not a universal donor.

Thus, ii is the correct genotype for the universal donor.