Question

Which of the following characteristics represents ‘inheritance of blood groups in humans?
a. Dominance.
b. Codominance.
c. Multiple allele.
d. Incomplete dominance.
e. Polygenic inheritance.

A. b, d and e.
B. b, c and e.
C, a, c and e.
D., a, b and c.

Answer 1

Blood groups are inherited from both parents. The ABO blood is controlled by a single gene in the DNA known as the ABO gene. In this ABO gene, three types of alleles exist that makes the genetic constituents of blood type. First and second are IA, and IB respectively, and third is the absence of these two antigen (i.e. O) .The ‘I’ stands for isoagglutinogen, also known as antigen.

Complete answer:
Dominance in different alleles of gene (I) -Since humans are diploid, each person possesses any two of the three genes and alleles. Wherein IA and IB are completely dominant over i, but when IA and IB are present together, they both express their own types of sugar and none is dominant over the other. This is called codominance and RBCs have both A and B types of proteins.

Codominance occurs in the blood groups system when both A and B antigens are present (one from each parent) and for the blood group AB. The offspring resembles both parents' blood types, and then it is called codominance. Different types of a red blood cell that makes ABO blood groups are-

Dominance - (IAIO, IBIO) - In an individual containing two allelic forms of a gene, one is expressed to the exclusion of the other.
Codominance - (IAIB) - a form of dominance where in the alleles of a gene pair in a heterozygote is fully expressed. In which the offspring has a phenotype that is neither dominant nor recessive.
Multiple allele- IA, IB & IO - 3-different allelic forms of a gene.

Hence, the correct answer is option (D).

Note: In the ABO Blood Group system, the A and B genes are codominant, i.e. both A and B occur at the same time. If there are neither A nor B then, O gene is present. Hence, incomplete dominance is not there in the ABO system, but codominance is present.
Polygenic inheritance is not there in the human blood group system as three alleles are responsible for the different types of blood groups in humans which is the property of multiple allelism.