How does the gene 'I' control ABO blood group in humans?

Allele from parent 1 Allele from parent 2 Genotype of offspring Blood type of offspring
IA
IA
IAIA
A
IA
IB
IAIB
AB
IA
i
IAi
A
IB
IB
IBIB
B
IB
i
IBi
B
i
i
ii
O
In humans, the ABO blood groups are controlled by a gene called gene. It has three alleles, namely IA, IB and i. A person possesses any two of the three alleles. IA and IB dominate over i. But with each other, IA and IB are co-dominant. The above table shows the genetic basis of blood groups in human population. These alleles helps to determine the blood group of a person. The plasma membrane of red blood cells has glycoproteins that protrude out from its surface which is regulated by the gene 'I' of ABO blood group. The alleles IA and IB produce A and B types of sugar, while allele i does not produce any sugar.