Biology 9700 · AS & A Level · Passage of information from parents to offspring
Passage of information from parents to offspring — practice question
Canavan disease is an inherited condition that is not sex-linked and causes progressive damage to neurones in the brain. Symptoms of the condition include loss of motor skills and mental retardation. These symptoms appear in early infancy, and many children with this condition die by the age of four years.
People with Canavan disease do not have an enzyme called aspartoacylase, which breaks down N-acetyl aspartate. The accumulation of N-acetyl aspartate can interfere with the formation of the myelin sheath, especially in neurones of the brain.
(a)[2]
Enzymes such as aspartoacylase show specificity. Outline what is meant by specificity of an enzyme.
(b)[3]
Complete the genetic diagram below to show how a man and a woman who are both unaffected could produce a child with Canavan disease.
(c)[3]
Explain the role of the myelin sheath in the functioning of a neurone.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “enzyme that is specific to a single substrate” …