Question

ABO blood grouping is controlled by gene I which has three alleles and show co-dominance. There are six genotypes. How many phenotypes in all are possible?

• A. Five
• B. Six
• C. Three
• D. Four

Answer 1

The correct option is D Four

Human blood group inheritance is the example of codominance and multiple alleles. It is governed by three alleles namely I${}^A$, I${}^B$ and i. I${}^A$ and I${}^B$ show codominance while allele "i" is recessive to both "I${}^A$" and "I${}^B$". This gives total six genotypes and four phenotypes- A (I${}^A$ I${}^A$ and I${}^A$i), B (I${}^B$ I${}^B$ and I${}^B$i), AB (I${}^A$ I${}^B$) and O (ii). Thus, the correct answer is option D.