(1) The gene (I) has three alleles
(2) A person will have only two of the three alleles
(3) When IA and IB are present together, they express same type of sugar.
(4) Allele ‘I’ does not produce any sugar.
Solution:
The correct option is C:
The gene that controls ABO blood groups, known as the ABO gene, has three alleles: IA, IB, and i. IA and IB encode enzymes that add specific sugars to a carbohydrate called H antigen, which is found on the surface of red blood cells. IA encodes an enzyme that adds a sugar called N-acetyl galactosamine to H antigen, while IB encodes an enzyme that adds a sugar called galactose. The presence of these sugars determines an individual’s ABO blood group: if IA is present, the individual will be blood group A; if IB is present, the individual will be blood group B; if both IA and IB are present, the individual will be blood group AB; and if neither IA nor IB is present, the individual will be blood group O.
Allele I does not encode an enzyme that adds a sugar to H antigen, and therefore individuals who have two copies of the I allele (ii genotype) do not have any sugars added to their H antigen.
Hence the wrong statement is When IA and IB are present together, they
express same type of sugar.