Question

Which of the following statements is/are correct about the inheritance of genes involved in human ABO blood grouping?

• A. It is inherited by complete dominant allele.
• B. It is inherited by complete recessive allele.
• C. It is inherited by co-dominant allele.
• D. All of the above.

Answer 1

Answer: (C)

It is inherited by co-dominant allele.

In human, ABO blood groups are controlled by gene I. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene I have three alleles or versions. I${}^A$, I${}^B$, and i. The alleles I${}^A$ and I${}^B$ produce the slightly different form of the sugar while allele i does not produce any sugar. Because humans are diploid organisms, each person possesses any two of the three I gene alleles. When I ${}^A$ and i are present only I${}^A$. expresses and when I ${}^B$ and i are present only I ${}^B$ is expressed because i don’t produce any sugar. But when. I${}^A$ and I ${}^B$ are present together they both express their own types of sugars. This is called codominance. Since there are three different alleles, there are six different combinations of three allies are possible, and therefore six different genotypes of human ABO blood types are seen.This shows that A & B are dominant genes and O (i) is the recessive gene. When two dominant genes are expressed together, it is called codominance.

Thus, the correct answer is option C.