Which factor primarily influences a person's AB blood type?

AB blood type is primarily influenced by genetics because it is determined by the alleles an individual inherits from their parents. Blood types are based on the presence or absence of specific antigens on the surface of red blood cells. For AB blood type, an individual must inherit one allele for A and one allele for B from their parents. This genetic inheritance follows Mendelian patterns, where the combinations of alleles from both parents determine the resulting blood type.

While environmental factors can play a role in many aspects of health and traits, they do not influence the specific genetic makeup that determines blood type. The presence of A and B antigens is a direct result of genetic coding, making genetics the key factor influencing a person's blood type.