Paper 2 H - SAMPLE SET 1 Q6
6) Huntington’s disease is an inherited disorder that affects the nervous system.
It is caused by a dominant allele.
A man is heterozygous for Huntington’s disease.
His partner is healthy and does not have the allele that causes Huntington’s disease.
6.1) What are the genotypes of the man and the woman? Use:
Woman’s genotype ______________________
6.2) The couple want to have a child.
Use a Punnett square to determine the probability of the child having Huntington’s disease.
Circle the genotypes of any children that will have Huntington’s disease. [4 marks]
It is caused by a dominant allele.
A man is heterozygous for Huntington’s disease.
His partner is healthy and does not have the allele that causes Huntington’s disease.
6.1) What are the genotypes of the man and the woman? Use:
- H for the allele that causes Huntington’s disease
- h for the healthy allele. [1 mark]
Woman’s genotype ______________________
6.2) The couple want to have a child.
Use a Punnett square to determine the probability of the child having Huntington’s disease.
Circle the genotypes of any children that will have Huntington’s disease. [4 marks]
Probability of child having Huntington’s disease = ____________
6.3) The couple visit a genetic counsellor, who gives them the following options.
The couple decide they want to have a healthy baby that is their own biological offspring.
Evaluate the options.
Suggest which option would be best for the couple. [6 marks]
(Total for Question 6 = 11 marks)
- Adopt a child.
- Gamete donation – uses sperm from another man to fertilise the woman’s eggs by in vitro fertilisation (IVF).
- Conceive naturally.
- Use pre-implantation genetic diagnosis (PGD).
• Many embryos are produced by IVF using gametes from the man and woman.
• Embryos are tested for Huntington’s disease and a healthy embryo is implanted into the woman’s uterus.
• The risk of implanting an embryo with the allele for Huntington’s disease is 0.2%.
• Costs the NHS about £11 000. - Conceive naturally and use prenatal diagnosis (PND) once the woman becomes pregnant.
• A sample of the placenta is taken at 10 weeks of pregnancy or a sample of fluid is taken from around the developing baby at 16 weeks of pregnancy.
• The sample is tested for the Huntington’s allele.
• A 0.5–1.0% risk of miscarriage.
• About 1% of samples collected are unsuitable for testing.
• Costs the NHS about £600.
The couple decide they want to have a healthy baby that is their own biological offspring.
Evaluate the options.
Suggest which option would be best for the couple. [6 marks]
(Total for Question 6 = 11 marks)