IB Biology SL D3.2.12 Haemophilia Questions

Use X-linked allele notation and Punnett grids to explain haemophilia inheritance and sex-specific risk in IB Biology SL D3.2.12.

Exam points

Explain haemophilia as an X-linked recessive disorder, using X-linked allele notation to identify carrier females and affected males.
Use an X-linked Punnett grid to predict offspring genotypes, phenotypes and sex-specific haemophilia risks.

[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.

	Father: $X^{H}$	Father: $Y$
Mother: $X^{h}$	$X^{H}X^{h}$	$X^{h}Y$
Mother: $X^{H}$	$X^{H}X^{H}$	$X^{H}Y$

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.

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IB Biology SL D3.2.12 Haemophilia Questions question 1