Question

Which of the following is true for dominant and recessive relationship of allele is case of human blood groups?
(Here ' >' represents dominance over other and '=' represents co-dominance)

• A. $I^A>I^B>I^O$
• B. $I^A=I^B=I^O$
• C. $I^A>I^B=I^0$
• D. $I^A=I^B>I^O$

Answer 1

The correct option is D

$I^A=I^B>I^O$

The gene for blood group is represented by letter $I$. It has 3 allelic forms - $I^A,I^B,I^O$.
It is a case of multiple alleles where a gene has more than two alternative alleles occupying the same locus on a chromosome or its homologue. $I^A$ and $I^B$ are co-dominant in nature. They express in both homozygous and heterozygous conditions. Whereas $I^O$ express itself only in homozygous condition and so $I^O$ is recessive in nature, i.e., $I^A$ and $I^B$ are dominant over $I^O$. Hence, the correction option is$I^A=I^B>I^O$.