In human genetics, the ABO blood group system is controlled by multiple alleles (I^A, I^B,… — JAMB UTME

In human genetics, the ABO blood group system is controlled by multiple alleles ( $I^A$ , $I^B$ , and $i$ ). Which of the following blood group phenotypes directly demonstrates codominance between alleles?

Blood group ABAnswer
B
Blood group O
C
Blood group A
D
Blood group B

Answer

Blood group AB

Blood group AB is determined by the heterozygous genotype

I^A I^B

. In this condition, both alleles

I^A

and

I^B

are fully and simultaneously expressed on red blood cell membranes without masking each other, making it a classic example of codominance.

Step-by-Step Solution

Define codominance in contrast to complete dominance and recessiveness.

Codominance occurs when two different alleles at a locus are both fully expressed in the heterozygous condition, resulting in a phenotype that displays both traits simultaneously.

Identifying the phenotypic expression of heterozygous genotypes determines the inheritance pattern.

Analyze the allele interactions in the ABO blood group system.

Alleles

I^A

and

I^B

are both completely dominant over allele

i

, but are codominant to each other.

Evaluating the relationship between alleles clarifies which genotype produces a codominant phenotype.

Determine which phenotype expresses both functional alleles simultaneously.

An individual with blood group AB has the genotype

I^A I^B

and produces both A and B antigens on red blood cells.

The presence of both distinct antigens demonstrates codominance.

Key Concept

Codominant Allele Expression in ABO Blood Group System

Estimated Time:45s

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