Understanding Codominance: Exploring the Case of ABO Blood Group System

A condition in which both alleles for a gene are fully expressed

The condition in which both alleles for a gene are fully expressed is referred to as codominance

The condition in which both alleles for a gene are fully expressed is referred to as codominance. In codominance, neither allele is dominant over the other, and as a result, both alleles are fully expressed in the phenotype of the individual.

To understand codominance better, let’s consider an example. One classic example of codominance is seen in the inheritance of blood type in humans. The ABO blood groups are determined by three alleles: A, B, and O. The A and B alleles are both codominant, meaning that when an individual inherits both A and B alleles, they will express both types of antigens on their red blood cells.

If an individual has the genotype AO (one A allele and one O allele) or BO (one B allele and one O allele), their blood type will be determined by the expression of the A or B allele, respectively. However, when an individual has the genotype AB (one A allele and one B allele), they will express both types of antigens (A and B) on their red blood cells. This is a clear example of codominance because both alleles (A and B) are fully expressed, and neither allele is dominant over the other.

In summary, codominance occurs when both alleles for a gene are fully expressed, resulting in a phenotype that shows traits from both alleles equally. The classic example of codominance is the ABO blood group system, where the A and B alleles are codominant, and individuals with the AB genotype express both A and B antigens on their red blood cells.

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