The expression of two different alleles of the same gene simultaneously in the heterozygote is called

The expression of two different alleles of the same gene simultaneously in the heterozygote is called codominance. In codominance, both alleles in a heterozygous individual contribute to the phenotype, meaning that both traits are fully expressed. A classic example of codominance can be seen in the ABO blood group, where blood type AB exhibits characteristics of both A and B alleles. This phenomenon contrasts with incomplete dominance, where the traits blend together in the phenotype, and simple dominance, where one allele completely masks the expression of the other. Understanding codominance is essential in genetics as it helps explain the complexity of inheritance patterns.