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Cystic fibrosis is a genetic disorder caused by recessive alleles - Edexcel - GCSE Biology - Question 2 - 2011 - Paper 1
Question 2
Cystic fibrosis is a genetic disorder caused by recessive alleles. The diagram shows the inheritance of cystic fibrosis in a family. (a) State the number of offspri... show full transcript
Worked Solution & Example Answer:Cystic fibrosis is a genetic disorder caused by recessive alleles - Edexcel - GCSE Biology - Question 2 - 2011 - Paper 1
Step 1
State the number of offspring in generation III who will have the disorder cystic fibrosis.
Answer
Based on the diagram provided, generation III has two affected individuals. Since cystic fibrosis is a recessive disorder, an individual must inherit two recessive alleles (bb) to express the condition. Therefore, there are 2 offspring in generation III with cystic fibrosis.
Step 2
Complete the sentence by putting a cross (✗) in the box next to your answer.
Answer
In generation III, individual 3 is:
✗ A. a carrier of the cystic fibrosis allele
Explanation: Individual 3 inherits one recessive allele from each of the parents who are either carriers or affected. This makes individual 3 a carrier.