What is the inheritance pattern for the AB blood type phenotype?

The AB blood type phenotype demonstrates a co-dominant inheritance pattern. In terms of genetics, co-dominance occurs when two different alleles are expressed simultaneously in an individual, resulting in a phenotype that is a combination of both traits. In the case of blood type, the alleles IA (which contributes to type A) and IB (which contributes to type B) are both present in an individual with the AB phenotype.

When an individual inherits one IA allele from one parent and one IB allele from the other, both alleles manifest equally, leading to the AB blood type. This differs from a recessive or dominant inheritance pattern, where one allele would overshadow the other, resulting in a single phenotype. The term "autosomal" refers more to the location of genes on the chromosomes rather than their expression patterns, so while blood type is indeed determined by genes located on autosomes, it does not directly pertain to the expression seen in the AB phenotype. Thus, co-dominance accurately describes how both IA and IB contribute to the visible AB blood type.