Question

“Gopalan argues that if father is of A blood group, mother is of B blood group. Their children can only be A group, B group or AB group.”
1) Do you agree with Gopalan’s argument?
2) Give reason for your answer.

Answer 1

Hint: The human ABO blood group is the example of codominance. According to this the ABO blood groups are controlled by the gene ‘I’. The plasma membrane of the RBCs has sugar polymers that protrude from its surface. The kind of sugar present on the plasma membrane is controlled by the I gene.

Complete step-by-step solution:
ABO blood groups are controlled by the I gene that is having three alleles${I^A},{I^B},{I^O}$or ‘i’ gene. Thus, it is considered as an example of multiple alleles also. Alleles${I^A}$and${I^B}$produce a slightly different form of sugar while${I^O}$ or i allele produces no sugar.
Since the human has a diploid set of chromosomes thus each person possesses any two of the three I gene alleles. Among the three alleles ${I^A},{I^B}$are completely dominant over I allele.
In the case of Gopalan’s argument different cases are formed like:
If the father has A blood group with allele ${I^A}{I^A}$and mother with allele${I^B}{I^B}$then

	${I^A}$	${I^A}$
${I^B}$	${I^A}{I^B}$	${I^A}{I^B}$
${I^B}$	${I^A}{I^B}$	${I^A}{I^B}$

 Thus, all the offspring have AB type of blood group.

>If the father has A blood group with allele${I^A}{I^A}$and mother with allele ${I^B}{I^O}$ then

	${I^A}$	${I^A}$
${I^B}$	${I^A}{I^B}$	${I^A}{I^B}$
${I^O}$	${I^A}{I^O}$	${I^A}{I^O}$

Thus, the offspring has either AB type of blood group or A blood group.

>If the father has A blood group with allele ${I^A}{I^O}$and mother with allele ${I^B}{I^B}$then

	${I^A}$	${I^O}$
${I^B}$	${I^A}{I^B}$	${I^O}{I^B}$
${I^B}$	${I^A}{I^B}$	${I^O}{I^B}$

Thus, the offspring has either B blood group or AB blood group.

>If the father has A blood group with allele ${I^A}{I^O}$and mother with allele${I^B}{I^O}$then

	${I^A}$	${I^O}$
${I^B}$	${I^A}{I^B}$	${I^O}{I^B}$
${I^O}$	${I^A}{I^O}$	${I^O}{I^O}$

Thus, the offspring have four types of blood group whether it is A or B or AB or O type of blood group.
So, the Gopalan’s argument is partially correct that the offspring have A, B or AB blood groups because besides all these 3 blood groups there is also a possibility of getting an O blood group.

Note: Multiple alleles is defined as the condition in which two or three alleles are present on the same locus of the chromosome. Multiple alleles are used to study the traits at the population levels. In the blood group, if ${I^A},{I^B}$are present together then both express themselves. Thus, it is considered as an example of codominance.