ABO blood grouping in humans is an example of codominance. ABO blood groups are controlled by gene I . Gene I has three alleles and and are the dominant alleles. When and are present together, both express equally and produce the surface antigens A and B , whereas is the recessive allele and does not produce any antigen. Pleiotropy referred to the genetic effect of a single gene on multiple phenotypic traits. Incomplete dominance is a genetic term in which a dominant allele does not completely dominate another allele, i.e., recessive. Segregation is the separation of allele during the process of gametogenesis. This is the basis of reappearance of recessive character in -generation

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