IB Biology SL 2.5.12 Sex-linked inheritance and haemophilia Question Bank
Practise IB Biology SL 2.5.12 by using pedigrees and Punnett grids to analyse haemophilia inheritance.
- Syllabus
- First assessment 2025
- Course
- Biology SL
- Level
- SL
Exam points
- Explain why males and females inherit X-linked recessive alleles differently.
- Use pedigree and Punnett-grid evidence to predict haemophilia outcomes.
D3.2.12—Haemophilia question 1
[Maximum number: 3]
People with the inherited disease hemophilia have a deficiency in one of the proteins that act as clotting factors in blood.
A family has a history of hemophilia that is caused by a sex-linked recessive allele. A woman from this family is a carrier and marries a man who does not have the allele. Showing your working, determine the probability of their children having the disease.
Alleles clearly labelled for both parents, in a Punnett square or other format.
Correct genotypes for all four possibilities for children.
Phenotypes of the children:
The sons would have a 50% chance of having hemophilia.
The daughters would have a 0% chance of having hemophilia / 50% chance of being a carrier.
Sex needs to be mentioned for this marking point, but information can be taken from the Punnett square.
[3]
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