Question

$ABO$ blood group is a good example of
A. Multiple alleles
B. Incomplete dominance
C. Codominance
D. Complete dominance

• A. (A) and (C) only
• B. (B) and (D) only
• C. (D) only
• D. (A), (C) and (D) only

Answer 1

Answer: (D)

According to the Law of Dominance, in a heterozygous organism, only the dominant allele expresses itself.
According to the Co-dominance Law, in a heterozygous organism, both dominant and recessive allele expresses themselves fully.
In incomplete dominance, both alleles express themselves partially.
Blood group is an example of Co-dominance, Complete dominance and Multiple alleles.
The gene I control the ABO blood groups. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind sugar is controlled by the gene. The gene (I) has three alleles I^A, I^B and i/I^O (Multiple alleles), where I^A and I^B are the dominant alleles and I^O/i is the recessive one. If I^A and I^B present together, then both of them will express resulting in AB blood group. But if, I^A or I^B is present with the recessive allele I^O/i, then the resulting blood group is going to be A or B respectively; this shows Mendel's law of dominance.
Though there is the presence of three alleles of the same gene in a population, an individual (2n) can have only two alleles. Therefore, multiple alleles can be detected only in a population. Since there are three different alleles, therefore six different genotypes are possible for the character (I^AI^A,I^AIO ;I^BI^B ; I^BI^O ; ,I^AI^B ; I^OI^O or ii). Thus, six genotypes and four phenotypes are possible.