Question

The ABO blood system exhibits a. codominance. b. multiple alleles. c. incomplete dominance. d. Both a and b are correct.

Short answer

The ABO blood system exhibits both codominance (in the case of blood type AB) and multiple alleles (with the presence of A, B, and O alleles). Therefore, the correct answer is: d. Both a and b are correct.

Step-by-step solution

Understand Codominance

In codominance, both alleles of a gene have an equal and observable effect on the phenotype. The offspring who inherit these alleles show a combination of both traits in their phenotype. In the ABO blood system, blood type AB is an example of codominance because it exhibits the attributes of both A and B antigens.

Understand Multiple Alleles

Multiple alleles refer to the presence of more than two alleles for a particular gene in a population. In the case of the ABO blood system, there are three different alleles: A, B, and O. These three alleles account for four possible blood types: A, B, AB, and O. The presence of three alleles is a clear indication that the ABO blood system exhibits multiple alleles.

Understand Incomplete Dominance

In incomplete dominance, neither allele is dominant over the other, and the phenotype expression is an intermediate between the two alleles. This type of dominance can be observed in the blending of traits, like the color of flowers. However, the ABO blood system does not exhibit incomplete dominance because blood type AB includes both the A and B antigens without blending or intermediate expression.

Relate the Dominance Types to the ABO Blood System

Looking at different types of dominance in the context of the ABO blood system, it is apparent that the system exhibits both codominance (in the case of blood type AB) and multiple alleles (with the presence of A, B, and O alleles). Therefore, the correct answer is: d. Both a and b are correct.