Question

ABO blood group is an example of
A. Epistasis
B. Multiple allelism
C. Pleiotropism
D. Complementary genes

Answer 1

Hint:
Genes are responsible for expression of different traits or characteristics in an organism. They are hereditary in nature which means the traits or characters contained in the genes are transferred from one generation to others. However, often due to various reasons the genes are unable to express normally and undergo certain changes which in turn induce changes in the expressed characters.

Complete answer:
The human blood contains several cells and the properties of these cells are determined by the antigens that are present or absent. The antigens cause to effect the different activities or behaviour of the erythrocytes or the blood cells. The antigens are present on the surface of the red blood cells. In addition to the antigens, some types of antibodies are also found which are associated with the antigens. This system of classification of human blood on the basis of presence or absence of antigens and antibodies are referred to as the ABO blood group system and it was discovered by Karl Landsteiner.
According to this system, blood groups in humans are of type A, type B, type O and type AB. The genes related to the blood groups are inherited from both the parents. The control of the ABO blood group is exerted by a single gene known as ABO gene. The ABO gene produces three types of alleles, which are i, IA and IB. Antigen is also known as isoagglutinogen and is referred to as I. The IA allele produces type A, IB produces type B and i gives type O. IA and IB alleles are dominant in nature over i allele. The individuals with IA IA will have type A blood group while IB IB will produce type B blood group. Due to the relationship of dominance of both these alleles, another type of blood group is found which is known as the AB type and the individual carrying this blood group contains both the alleles. This behaviour of the IA and IB inherited and expressed together is referred to as codominance.
The presence of more than two types of contrasting alleles for a gene is known as multiple allelism. In the human ABO blood group system, both the recessive and dominant characters are expressed when present in the heterozygous genotype. In this condition, the individual will show characteristics for both IA and IB alleles and the blood group will be AB blood group. The other allele i is recessive to both IA and IB. This condition is known as multiple allelism.
Epistasis is a phenomenon of masking or covering the genetic effects of one gene at apposition by another gene present at another locus. In this process of gene interaction, the expression of one gene is completely made inactive by another gene and the characters will not express side by side.
Pleiotropism is a condition where a single gene is capable of producing several or multiple effects. These traits may seem unrelated in nature. In this condition, a single gene affects two or more characters. Complementary genes are the genes which contribute towards a single characteristic. In this condition though two or more genes can contribute towards expression of a trait but they can also mask the effect of the other.

Thus, the correct option selected is option B.

Note: In the ABO blood system, three types of alleles are present in which two of the alleles are dominant in nature while one type is recessive. The alleles IA and IB are dominant in nature while i is recessive. When both the dominant alleles are present in an individual, both the alleles are expressed together. This condition of expression of the alleles is known as multiple allelism.