In human ABO blood groups, an individual carrying both the I^A and I^B alleles expresses b… — JAMB UTME

In human ABO blood groups, an individual carrying both the $I^A$ and $I^B$ alleles expresses both A and B antigens equally on the surface of red blood cells, demonstrating codominance.

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Answer

The statement is true. Individuals with genotype

I^A I^B

produce both A and B antigens on their red blood cells, showing full expression of both alleles.

Codominance refers to an inheritance pattern where two different alleles at a locus are both fully expressed in heterozygotes. In blood group AB (genotype

I^A I^B

), both A and B antigens exist on the erythrocyte membrane without blending or masking.

Step-by-Step Solution

Analyze the genetic relationship between the

I^A

and

I^B

alleles in human blood groups.

Both

I^A

and

I^B

alleles code for functional cell-surface enzymes that attach specific sugar antigens to red blood cells.

Understanding the allele actions determines the phenotypic outcome in heterozygotes.

Determine whether the inheritance pattern shown is codominance.

Because neither allele masks the other and both A and B antigens are fully expressed together in blood group AB, the pattern is codominance.

Codominance is defined by the joint and full expression of both alleles in a heterozygous organism.

Key Concept

Codominance in ABO Blood Grouping

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