Question

Why is human blood type an example of multiple alleles? codominance?

Answer 1

When alleles show a co-dominant relationship neither alleles is dominant and both are expressed in the phenotype of the heterozygote. The human body ABO blood groups provide a good example of codominance, The ABO system is due to a gene that codes of molecules on the surface of red blood cells.
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Answer 2

It is because when alleles show a co-dominant relationship , neither allele is dominant and both are expressed in the phenotype of the heterozygote. The human ABO blood groups provide a good example of codominace. The ABO system is due to a gene that codes for molecules on the surface of red blood cells