A cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together. Blood type AB.

It is called codominance

Explanation: Every trait is controlled by at least a pair of gene. Genes have different forms known as alleles. Codominance is a heterozygous condition in which two alleles at a gene locus are fully and equally expressed in the phenotype of the organism. The alleles that express themselves equally are called codominant alleles. Neither of the alleles is fully dominant over the other in codominance.

Example is in the ABO blood group in which A is dominant and B is also dominant and AB is codominant while O is recessive.