D3.2.10—Incomplete dominance and codominance

Incomplete dominance blends heterozygote phenotype, while codominance expresses both alleles fully in the heterozygote in inheritance problems in inheritance problems.

Exam analysis

Chance of appearing3%of analysed past papers

Latest appearanceNovember 2019

Most common paperPaper1

Typical marks1–6

Common command terms

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Describe

Recent exam appearances

November 2019Paper1 ["HL"] · TZ013[ 1 ]D3.2.10—Incomplete dominance and codominance

November 2014Paper2 ["HL"] · TZ07(b)[ 6 ]D3.2.10—Incomplete dominance and codominance

May 2014Paper1 ["HL"] · TZ111[ 1 ]D3.2.10—Incomplete dominance and codominance

Practice this objective

Coverage 2014–2019 · Updated 16 Jul 2026

Concept essentials

Incomplete dominance produces an intermediate heterozygote phenotype.
Codominance expresses both alleles in the heterozygote.
Non-Mendelian allele relationships can make phenotype ratios match genotype ratios.

ConceptIB Biology HL