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
- HL
Exam analysis
Chance of appearing9%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper1
Typical marks1
Common command terms
- Describe
- State
- Identify
- Outline
Recent exam appearances
November 2023Paper1 ["HL"] · TZ236[ 1 ]D3.2.9—ABO blood groups
May 2023Paper1 ["HL"] · TZ134[ 1 ]D3.2.9—ABO blood groups
November 2022Paper1 ["HL"] · TZ011[ 1 ]D3.2.9—ABO blood groups
May 2021Paper2 ["HL"] · TZ17(a)[ 4 ]D3.2.9—ABO blood groups
November 2020Paper1 ["HL"] · TZ011[ 1 ]D3.2.9—ABO blood groups
Practice this objective
Coverage 2013–2023 · 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.