Question

Inheritance of blood group is
(a) Codominance
(b) Incomplete dominance
(c) Multiple allelism
(d) Multiple gene

• A. a, b
• B. b, d
• C. a, c
• D. b, c
• E. a, d

Answer 1

Answer: (C)

a, c

A multiple gene trait is controlled by more than one genes while multiple allelism is the condition where a trait is controlled by more than two alleles of a gene. Human blood group is governed by single gene I which has three alleles I${}^A$, I${}^B$ and I${}^O$. This makes (d) wrong and (c) correct. The three alleles make total six genotypes I${}^A$ I${}^A$, I${}^A$ I${}^O$, I${}^B$ I${}^B$, I${}^B$ I${}^O$, I${}^A$ I${}^B$ and $I^O$$I^O$. Incomplete dominance is the condition when none of the factors of a gene is dominant, the phenotype of the heterozygous dominant individual is a blend of dominant and recessive traits. The genotypes I${}^A$I${}^O$ and I${}^B$I${}^O$ gives A and B blood group respectively which means that I${}^A$ and I${}^B$ alleles are dominant over I${}^O$ allele and mask the effect of later; none of the heterozygote show blend of recessive and dominant trait which makes (b) wrong. The genotype I${}^A$ and I${}^B$ produce AB blood group which means that I${}^A$ and I${}^B$ alleles are codominant. When both recessive and dominant traits are expressed in a heterozygous genotype; it is codominance; this makes (a) correct.

Thus, the correct answer is option C.