The phenotype of a heterozygous organism showing an intermediate trait is due to:

• A. Complete dominance
• B. Incomplete dominance
• C. Codominance
• D. Polygenic inheritance

Answer: (B)

Incomplete dominance occurs when neither allele fully dominates the other, so the heterozygote shows a blended phenotype between the two homozygous forms. This happens because the gene products from each allele are present at intermediate levels, yielding an intermediate trait rather than the full expression of one allele. A classic example is red and white flowers producing pink offspring, illustrating the blend. This differs from complete dominance, where the dominant allele masks the other; from codominance, where both alleles are expressed fully and separately (as in distinct markers or colors on the same organism); and from polygenic inheritance, where many genes influence a trait to produce a continuous range.