The diagram shows a family considering genetic screening before having another child. Their first child has cystic fibrosis, caused by a recessive allele. A...
Question 1 Report
The diagram shows a family considering genetic screening before having another child. Their first child has cystic fibrosis, caused by a recessive allele. A nurse takes a small blood sample from each parent and tests DNA from their white blood cells. Fig. 1 includes a genetic diagram for the two parents. Neither parent has the disease, but both are carriers. The couple are given counselling before they decide whether to have tests during a future pregnancy.
(a) Identify the genotype of a carrier of cystic fibrosis. [1]
(b) Calculate the probability that the couple's next child will have cystic fibrosis. [2]
(c) Explain two reasons why genetic counselling is important before screening an unborn child. [2]
Answer Details
(a) Ff [1] (b) One ff box out of four [1]; 1/4 / 25% [1] (c) Any two: results may cause anxiety or difficult decisions [1]; parents need to understand probabilities and limits of the test [1]; screening may reveal information about other family members [1].
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