1. 1
   A genetics clinic keeps anonymised records of family inheritance patterns to help explain genetic disorders to patients. One record concerns a family affected by polydactyly, a condition caused by a dominant allele that results in extra fingers or toes.

   (a)

   A genetics clinic records that polydactyly (having extra fingers or toes) is caused by a dominant allele. A man with polydactyly, who is heterozygous for the allele, has children with a woman who does not have polydactyly. What proportion of their children would be expected to have polydactyly?

   [1 mark]

   • A0%
   • B25%
   • C50%
   • D100%

   (b)

   Cystic fibrosis is caused by a recessive allele. Two parents, both unaffected by cystic fibrosis, have a child who has cystic fibrosis. What does this tell the clinic about the genotypes of the parents?

   [1 mark]

   • ABoth parents must be homozygous dominant
   • BBoth parents must be heterozygous carriers
   • COne parent must be homozygous recessive
   • DThe child's genotype gives no information about the parents

   (c)

   The clinic also records a family in which sickle cell anaemia, caused by a recessive allele, appears in a child even though neither parent has the condition. Explain, using the terms genotype and phenotype, why two unaffected parents can have a child with sickle cell anaemia.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A national population screening survey collects anonymised data on chromosome numbers and single-gene conditions in newborn babies, to monitor the frequency of different types of inherited disorder.

   (a)

   A national population screening survey records the number of chromosomes in cells from newborn babies. One baby's cells are found to contain 47 chromosomes instead of the usual 46, with an extra copy of one chromosome. Which condition is this abnormality most closely associated with?

   [1 mark]

   • ACystic fibrosis
   • BSickle cell anaemia
   • CPolydactyly
   • DDown's Syndrome

   (b)

   The survey also records babies with polydactyly, cystic fibrosis and sickle cell anaemia, which are all described as being caused by 'differences at the gene level' rather than by a change in chromosome number. Which statement correctly describes this difference between Down's Syndrome and the other three conditions?

   [1 mark]

   • ADown's Syndrome is caused by an extra chromosome, while the other three are caused by alleles of single genes
   • BDown's Syndrome is caused by an abnormal allele of a single gene, while the other three are caused by an extra chromosome
   • CAll four conditions are caused by an extra copy of a chromosome
   • DAll four conditions are caused by alleles of a single gene

   (c)

   The survey data shows that polydactyly, cystic fibrosis and sickle cell anaemia occur at broadly similar rates each year, while conditions caused by an abnormal chromosome number are far less common. Describe one similarity and one difference in how these two groups of inherited conditions arise.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A genetics clinic uses anonymised family trees, built from data volunteered by patients, to explain inheritance patterns for genetic disorders during genetic counselling sessions.

   (a)

   A genetics clinic constructs a family tree covering three generations to study the inheritance of cystic fibrosis. In this family, two unaffected grandparents have an unaffected son. This son has children with an unaffected woman from outside the family, and one of their three children has cystic fibrosis. Use this information to explain what the genotypes of the son and his partner must be, and state the probability that any one of their children will have cystic fibrosis.

   [3 marks]

   (b)

   In the same family tree, the clinic notes that the son's partner has a younger sibling with cystic fibrosis, even though the partner's own parents are both unaffected. Explain what this tells the clinic about the partner's parents' genotypes, and describe how the clinic could use a genetic diagram to represent this cross and predict the possible genotypes of any children.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A university research team studying public understanding of genetics is producing an information leaflet explaining how genetic disorders are inherited, based on anonymised population screening data.

   (a)

   A university research team is analysing anonymised population data on inherited disorders to produce public information material. They ask you to explain, for a general audience, how polydactyly, cystic fibrosis and sickle cell anaemia are each inherited, describing the roles of dominant and recessive alleles, genotype and phenotype in producing the pattern of inheritance seen for each condition.

   [6 marks]

   (b)

   The same research team also wants the leaflet to explain how a condition caused by an abnormal chromosome number, such as Down's Syndrome, differs from a condition caused by a single recessive allele, such as cystic fibrosis. Evaluate how useful data on family inheritance patterns is for predicting these two different types of inherited condition in future children.

   [6 marks]

   Total for question 4: 12 marks

End of questions