Co-dominance is best described as?

Co-dominance is best described as?

• A. Only one allele expressed
• B. Traits are blended
• C. Environment determines expression
• D. Both alleles are expressed; both traits are shown

Answer: (D)

Co-dominance means that in a heterozygous individual, both alleles are expressed and both traits appear at the same time. There isn’t a single dominant allele that masks the other; instead, each allele contributes to the phenotype. A classic example is the AB blood type, where the A and B antigens are both present on red blood cells, so the phenotype shows both traits. Another example is roan coat color in some cattle, where red and white hairs coexist rather than blending into a single intermediate color. This is different from incomplete dominance, where you’d see a blend (like pink from red and white). The expression is determined by the genetic alleles themselves, not by the environment.

Co-dominance means that in a heterozygous individual, both alleles are expressed and both traits appear at the same time. There isn’t a single dominant allele that masks the other; instead, each allele contributes to the phenotype.

A classic example is the AB blood type, where the A and B antigens are both present on red blood cells, so the phenotype shows both traits. Another example is roan coat color in some cattle, where red and white hairs coexist rather than blending into a single intermediate color. This is different from incomplete dominance, where you’d see a blend (like pink from red and white). The expression is determined by the genetic alleles themselves, not by the environment.