Genetic screening and ethical issuesEdexcel A-Level Biology A: Subtopic test

1. 1
   A couple who are both carriers of the cystic fibrosis (CF) allele are having fertility treatment. Eight embryos have been created outside the body. When each embryo reaches the eight-cell stage, one cell is removed and its DNA is tested for the CF allele. Only embryos that do not have CF will be placed in the woman's uterus.

   (a)

   What is the name of this type of genetic screening?

   [1 mark]

   • AAmniocentesis
   • BPre-implantation genetic diagnosis (PGD)
   • CChorionic villus sampling
   • DCarrier screening of the parents

   (b)

   On average, how many of the eight embryos would be expected not to have CF?

   [1 mark]

   • A2
   • B4
   • C8
   • D6

   (c)

   Explain why removing one cell at the eight-cell stage is unlikely to harm the development of the embryo.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A woman who already has a child with a serious recessive disorder is 12 weeks pregnant. She and her partner are both carriers. She has been offered either chorionic villus sampling (CVS) now, or amniocentesis at 16 weeks. Each procedure carries a risk of miscarriage of about 1%.

   (a)

   Which sample is taken in chorionic villus sampling?

   [1 mark]

   • AA small piece of tissue from the placenta
   • BAmniotic fluid from around the fetus
   • CBlood from the mother's arm
   • DA cell from an embryo made by IVF

   (b)

   What is an advantage of CVS compared with amniocentesis?

   [1 mark]

   • AIt carries no risk of miscarriage
   • BIt does not involve passing an instrument into the uterus
   • CIt can be done earlier in the pregnancy, so the results are available sooner
   • DIt tests the mother's DNA rather than the fetus's DNA

   (c)

   Suggest two reasons why the woman might decide not to have either test.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A region has a high frequency of a serious recessive blood disorder. The local health authority offers free carrier screening to all adults who plan to have children. A cheek swab is taken and the DNA is tested for the faulty allele. People found to be carriers are offered genetic counselling.

   (a)

   Explain how carrier screening and genetic counselling help couples to make informed decisions about having children.

   [3 marks]

   (b)

   Discuss two social or ethical concerns about a population carrier screening programme like this one.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A couple who are both carriers of a serious recessive condition ask a fertility clinic to use pre-implantation genetic diagnosis (PGD). The other option open to them is to conceive naturally and use prenatal testing, deciding whether to end the pregnancy if the fetus is affected. The clinic's ethics committee is meeting to consider the request and has asked for advice on the practical and ethical issues.

   (a)

   Evaluate the use of PGD compared with natural conception followed by prenatal testing for this couple.

   [6 marks]

   (b)

   Discuss the social and ethical issues, from a range of ethical viewpoints, that the committee should consider.

   [6 marks]

   Total for question 4: 12 marks

End of questions