To solve this problem, we need to analyze the statements regarding the gene 'I' that controls ABO blood groups and identify the incorrect one. Let's evaluate each option:$\newline \bullet$Option 1: A person will have only two of the three alleles.$\newline$ - The ABO blood group system is controlled by a single gene with three alleles: $I^A, I^B,$ and $i. \newline$ - Each individual inherits two alleles, one from each parent.$\newline$ - Therefore, this statement is correct.$\newline \bullet$Option 2: When $I^A$ and $I^B$ are present together, they express the same type of sugar.$\newline$ - $I^A$ and $I^B$ are codominant alleles, meaning both express their respective antigens when present together.$\newline$ - $I^A$ produces A antigen (N-acetylgalactosamine), and $I^B$ produces B antigen (galactose).$\newline$ - Therefore, this statement is incorrect as they express different sugars.$\newline \bullet$Option 3: Allele ‘i’ does not produce any sugar.$\newline$ - The allele 'i' is recessive and does not produce any antigen on the red blood cells.$\newline$ - Therefore, this statement is correct.$\newline \bullet$Option 4: The gene (I) has three alleles.$\newline$ - The ABO blood group system is indeed controlled by three alleles: $I^A, I^B,$ and $i. \newline$ - Therefore, this statement is correct.$\newline$Based on the analysis, the incorrect statement is Option 2.