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4. Haemophilia is a recessive sex-linked genetic disorder - Edexcel - GCSE Biology - Question 4 - 2016 - Paper 1
Question 4
4. Haemophilia is a recessive sex-linked genetic disorder. The letter h is used for the recessive allele and H for the dominant allele. The diagram shows the inher... show full transcript
Worked Solution & Example Answer:4. Haemophilia is a recessive sex-linked genetic disorder - Edexcel - GCSE Biology - Question 4 - 2016 - Paper 1
Step 1
Step 2
Calculate the probability of person F and person G having a child with haemophilia.
Answer
To find the probability of person F and person G having a child with haemophilia, we first determine their genotypes. Person F is assumed to be a homozygous recessive male (Y, X^h) for haemophilia, while person G, being a heterozygous female (X^H, X^h), can pass either allele.
Using a Punnett square:
| X^H | X^h | |
|---|---|---|
| X^h | X^H X^h | X^h X^h |
| Y | X^H Y | X^h Y |
From the Punnett square:
- X^H X^h: Heterozygous female (not affected)
- X^h X^h: Affected male (has haemophilia)
- X^H Y: Normal male (not affected)
- X^h Y: Affected male (has haemophilia)
The probabilities are:
- 2/4 are unaffected (X^H X^h, X^H Y)
- 2/4 have haemophilia (X^h X^h, X^h Y)
Thus, the probability of having a child with haemophilia is 2 out of 4, or 50%.