1. 1
   A plant breeder crosses two pea plants that are both heterozygous for flower colour. The purple flower allele (P) is dominant over the white flower allele (p). Both parent plants have the genotype Pp and produce a large number of offspring.

   (a)

   What is the phenotype of a plant with the genotype Pp?

   [1 mark]

   • AWhite flowers
   • BPurple flowers
   • CPink flowers
   • DNo flowers form

   (b)

   Which term describes a plant with the genotype Pp?

   [1 mark]

   • AHomozygous dominant
   • BHomozygous recessive
   • CHeterozygous
   • DHaploid

   (c)

   Using a genetic diagram, predict the ratio of purple-flowered to white-flowered offspring expected from this cross, and state the genotype(s) that would produce white flowers.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A father and mother, neither of whom has cystic fibrosis, have a child who is diagnosed with the condition shortly after birth. Cystic fibrosis is caused by a recessive allele (f) of a gene, with the dominant allele (F) not causing the disorder. Genetic testing shows that both parents carry one copy of the recessive allele.

   (a)

   What is the genotype of each parent?

   [1 mark]

   • AFF
   • BF only
   • Cff
   • DFf

   (b)

   What term describes an individual with genotype Ff who does not show symptoms of the disorder?

   [1 mark]

   • ADominant
   • BCarrier
   • CRecessive
   • DMutant

   (c)

   Using a genetic diagram or Punnett square reasoning, explain how two unaffected parents can have a child with cystic fibrosis, and state the probability that a child of these two parents will have the disorder.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the ABO blood group system in a family. The gene controlling ABO blood group has three alleles: I^A and I^B, which are codominant with each other, and I^O, which is recessive to both. A mother has blood group A with genotype I^A I^O, and a father has blood group B with genotype I^B I^O.

   (a)

   Explain what is meant by codominance and multiple alleles, using the ABO blood group system as an example.

   [3 marks]

   (b)

   Determine all the possible genotypes and phenotypes (blood groups) that could occur among the children of the mother (I^A I^O) and father (I^B I^O) described above.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Red-green colour blindness is caused by a recessive allele carried on the X chromosome. A woman who is a carrier for the condition, and who has normal colour vision, has children with a man who has normal colour vision and does not carry the allele. Genetic counsellors use knowledge of inheritance patterns like this, alongside information from the Human Genome Project, to advise families about the likelihood of inherited conditions appearing in their children.

   (a)

   Explain how red-green colour blindness is inherited in this family, including why the condition is much more common in males than in females. Use genetic diagram reasoning in your answer.

   [6 marks]

   (b)

   Discuss how understanding inheritance patterns such as this, combined with outcomes of the Human Genome Project, could be used by genetic counsellors to advise this family, and evaluate one potential benefit and one potential limitation of using genetic information in this way.

   [6 marks]

   Total for question 4: 12 marks

End of questions