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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
In generation III, there are two affected individuals, which indicates that they each must have received the recessive allele for cystic fibrosis from their parents. According to the provided diagram, there is a total of 4 offspring in generation III. Therefore, the answer is 2 offspring who will have 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 carrier of the cystic fibrosis allele
This is because individual 3 must have inherited one recessive allele for cystic fibrosis from one parent and a dominant allele from the other parent, making them heterozygous.