Ace Abeka Biology Test 3 in 2026 – Dive Into Discovery and Smash It!

When looking at how alleles are expressed in a heterozygous individual, codominance is the pattern where both alleles are shown fully and at once in the phenotype. A classic example is the ABO blood types: an individual with one A allele and one B allele expresses both A and B antigens, resulting in the AB blood type. This stands in contrast to incomplete dominance, where the heterozygote shows an intermediate trait (like a pink flower from red and white). It also differs from homozygous, where both alleles are the same, so only one form is produced, and from a dominant allele masking the other, where only the dominant trait appears.