when two different alleles are expressed at the same time
Best Answer: A recessive allele will not be expressed if it is in the presence of a dominant allele. The dominant allele covers up the recessive one. When two alleles are both expressed, two situations may occur: Incomplete dominance is when two alleles are epressed and blend to create a new, third phenotype.For example, when a red allele and white allele result in a pink flower. Codominance is when both alleles are expressed at the same time.In this case, a red allele and white allele result in aread and white spotted flower.hen two alleles are both expressed, two situations may occur: Incomplete dominance is when two alleles are epressed and blend to create a new, third phenotype. For example, when a red allele and white allele result in a pink flower.