D3.2.9—ABO blood groups
ABO blood groups depend on three alleles, with IA and IB codominant and both dominant over i in inheritance problems.
- Syllabus
- First assessment 2025
- Objective
- D3.2.9
- Level
- SL
Exam analysis
Chance of appearing14%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–3
Common command terms
- Describe
- State
- Identify
- Outline
Recent exam appearances
November 2025Paper1B ["SL"] · TZ34(d)[ 3 ]D3.2.9—ABO blood groups
November 2022Paper1 ["SL"] · TZ015[ 1 ]D3.2.9—ABO blood groups
May 2021Paper1 ["SL"] · TZ215[ 1 ]D3.2.9—ABO blood groups
November 2019Paper2 ["SL"] · TZ06(b)[ 4 ]D3.2.9—ABO blood groups
May 2019Paper1 ["SL"] · TZ215[ 1 ]D3.2.9—ABO blood groups
Practice this objective
Coverage 2010–2025 · Updated 16 Jul 2026
Concept essentials
- IA and IB are codominant in blood group AB.
- The i allele is recessive to both IA and IB.
- Blood group phenotype may correspond to more than one genotype.