Question

.For alleles controlling the ABO blood types, the relationship between the IA and i alleles is? The relationship between the IA and IB alleles is?

. a.Complete dominance, codominace

b.Codominance, complete dominance

c.Complete dominance, incomplete dominance

d.Incomplete dominance, codominance

Answer 1

Answer. (b)

As per the law of dominance, in a heterozygous condition one of the allele dominates over the other. The one which gets expressed is called the dominant allele while the one which gets suppressed is called recessive allele.

In case of incomplete dominance, the phenotype of the heterozygote is intermediate between the phenotype of the homozygous parents.

In codominanc, both the alleles are simultaneously expressed. there is no dominance-recessive relationship.

The ABO blood group in humans is an example of codominance.

Allele 1	Allele 2	Genotype	Phenotype
IA	IA	IAIA	A
IA	IB	IAIB	AB
IA	I	IAi	A
IB	IA	IBIA	AB
IB	IB	IBIB	B
IB	i	IAi	B
i	i	ii	O

Herein, the A and B blood group genes are codominant and in case of a heterozygote, both are expressed. O is however recessive to both A and B.

The A, B, O blood groups differ in the presence of surface antigens which are glycan moities present on the surface of RBCs.

In individuals with A blood group, A antigen is present on the surface of RBCs while the plasma contains anti-B antibodies.

In individuals with B blood group, B antigen is present on the surface of RBCs while the plasma contains anti-A antibodies.

In individuals with AB blood group, both A and B antigens are present on the surface of RBCs while the plasma contains no anti-A or anti-B antibodies.

In individuals with O blood group, no antigen is present on the surface of RBCs while the plasma contains both anti-A and anti-B antibodies.

AB blood group people are universal acceptors of blood while Individuals with O blood group are universal donors.