Key Concepts In codominance, both alleles are expressed equally in the phenotype of the heterozygote. For example, red cows crossed with white cows will have offspring that are roan cows. Roan refers to cows with red hair and white blotches. Many genes have multiple alleles An example is ABO blood type in humans. 3. Multiple Alleles Sometimes, even if only two alleles control a trait, there may actually be more than two types of alleles available. This will also lead to more than two phenotypes expressed. Another blood group system in humans, the ABO system, is an example of a character governed by multiple alleles. Three alleles are responsible for this blood system: P. and i The ABO blood type is determined by the presence or absence of two antigens, A and B. Allele / does not code for an antigen. There are four possible blood types as shown in Table 2 Table 2. Human ABO blood types and their phenotypes Blood Types A B AB O The 1 and 1 alleles are dominant over the i allele, which is always recessive However, when the 1 and 1 alleles are inherited together, both alleles are expressed equally. This also makes 1 and 1B codominants of each other. Activity 3: Objective: Materials: ji Genotypes What is your blood type? Do you know your blood type? What are your parents' blood types? paper pencil What's Your Blood Type? Infer the unknown phenotypes of individuals on the basis of the kn phenotypes of their family members blood types ​