Question

If two persons with 'AB' blood group marry and have sufficiently large number of children, these children could be classified as 'A' blood group : 'AB' blood group 'B' blood group in 1 : 2 : 1 ratio. Modern technique of protein electrophoresis reveals presence of both 'A' and 'B' type proteins in 'AB' blood group individuals. This is an example of :

• A. Complete dominance
• B. Codominance
• C. Incomplete dominance
• D. Partial dominance

Answer 1

The Correct Option is B

 The given question involves an understanding of genetics, specifically the concept of dominance in blood group inheritance. Let's analyze the scenario described:

An individual with 'AB' blood group genotype has both 'A' and 'B' alleles. In the case of another such individual marrying and having children, the possible genotypes of their children from genetic crosses (Punnett square) can be:

	A	B
A	AA	AB
B	AB	BB

From this cross, the genotype distribution of the children is as follows:

• \(1\) individual with 'AA' genotype (Blood Group 'A')
• \(2\) individuals with 'AB' genotype (Blood Group 'AB')
• \(1\) individual with 'BB' genotype (Blood Group 'B')

The phenotypic ratio obtained is 1 : 2 : 1 of Blood Group 'A' : 'AB' : 'B'.

In this context, 'AB' blood group individuals express both 'A' and 'B' antigens simultaneously. This equal expression of both alleles in the phenotype without one being dominant over the other is known as Codominance. Therefore, seeing both 'A' and 'B' proteins in 'AB' individuals is a classic case of codominance.

Thus, the correct answer is Codominance. Here is a brief explanation of why the other options are not applicable:

• Complete Dominance: This would occur if one allele completely masked the other, which is not the case here.
• Incomplete Dominance: This would involve a blending of traits, creating an intermediate phenotype, which also does not happen in this case.
• Partial Dominance: Similar to incomplete dominance, it involves intermediate expression, which does not apply to the 'AB' blood group scenario.