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Cystic fibrosis (CF) is a recessive genetic disorder - Edexcel - GCSE Biology - Question 2 - 2016 - Paper 1
Question 2
Cystic fibrosis (CF) is a recessive genetic disorder. Matthew and Selina both have the genotype Ff. They are carriers of this disorder. The diagram shows how CF was ... show full transcript
Worked Solution & Example Answer:Cystic fibrosis (CF) is a recessive genetic disorder - Edexcel - GCSE Biology - Question 2 - 2016 - Paper 1
Step 1
(a) (i) State the percentage of the male children with CF.
Answer
To determine the percentage of male children with cystic fibrosis (CF), we analyze the possible genotypes of the children.
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From Matthew (Ff) and Selina (Ff), the possible genotypes for their children can be:
- FF (homozygous dominant)
- Ff (heterozygous)
- ff (homozygous recessive)
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The breakdown is as follows:
- 25% - FF
- 50% - Ff
- 25% - ff
Among the three children depicted:
- Chris is ff (has CF)
- Stewart is FF (does not have CF)
- Megan is Ff (carrier, does not have CF)
Thus, only Chris, who is male, has CF. Since there are 3 male children (Chris and Stewart), the percentage of males with CF is:
rac{1}{2} imes 100 = 50\%
Step 2