Question

Blood grouping in human beings is controlled by

• A. 4 alleles in which A is dominant
• B. Alleles in which A and B are dominant, other is recessive
• C. 3 alleles in which none is dominan
• D. 3 alleles in which A is dominant
• E. 4 alleles in which none is dominant

Answer 1

The correct option is B Alleles in which A and B are dominant, other is recessive

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${}^O$. I${}^A$ and I${}^B$ show codominance while allele I${}^O$ is recessive to both I${}^A$ and I${}^B$. Both I${}^A$ and I${}^B$ are dominant over I${}^O$. This gives total six genotypes and four phenotypes - A (I${}^A$ I${}^A$ and I${}^A$ I${}^O$), B (I${}^B$ I${}^B$ and I${}^B$ I${}^O$), AB (I${}^A$ I${}^B$) and O (I${}^O$ I${}^O$). Correct option is "B".