How does blood type inheritance demonstrate co-dominance?

Blood type inheritance demonstrates co-dominance as both A and B alleles can be expressed simultaneously in the AB blood type.

In the context of blood types, co-dominance refers to the genetic scenario where both alleles (A and B) contribute to the phenotype of the organism. This is different from complete dominance, where one allele completely masks the effect of the other. In the case of blood types, the A and B alleles are co-dominant, and the O allele is recessive.

The ABO blood group system is determined by the ABO gene, which is found on chromosome 9. The gene has three alleles: A, B, and O. An individual inherits two alleles, one from each parent, which determines their blood type. If an individual inherits an A allele from one parent and a B allele from the other, they will have type AB blood. This is because the A and B alleles are co-dominant and both are expressed in the phenotype.

In contrast, if an individual inherits an A allele from one parent and an O allele from the other, they will have type A blood. This is because the A allele is dominant over the O allele, and the O allele is not expressed in the phenotype. Similarly, if an individual inherits a B allele and an O allele, they will have type B blood.

The co-dominance of the A and B alleles is also evident in the antigens present on the red blood cells. Individuals with type A blood have A antigens, those with type B blood have B antigens, and those with type AB blood have both A and B antigens. This is a direct result of the co-dominance of the A and B alleles.

In summary, blood type inheritance is a clear example of co-dominance, where both A and B alleles can be expressed simultaneously, resulting in the AB blood type. This is different from other genetic scenarios where one allele completely masks the effect of the other.