Biology 9700 · AS & A Level · Principles of genetic technology
Principles of genetic technology — practice question
Leber’s congenital amaurosis (LCA) is an autosomal recessive eye disease. It causes eye disorders present from birth, including severe loss of vision. LCA has been treated successfully by gene therapy, using a virus rather than a plasmid as the vector. Adeno-associated virus (AAV) vectors carrying the therapeutic allele were injected straight into the retina, the layer at the back of the eye that contains the photoreceptor cells. People who had been blind from a young age were able to see again. There is a risk linked to the injection technique used to deliver the vectors, because it could make the retina detach and so damage vision. This delivery method was first applied to LCA before being tested on other retinal diseases that gradually reduce people’s vision as they grow older.
(a(i))[4]
Suggest the main stages used to make recombinant DNA in this gene therapy example.
(a(ii))[2]
Explain why the fact that LCA is an autosomal recessive genetic disease makes it suitable for treatment with gene therapy.
(a(iii))[2]
Suggest why the retinal injection method of gene therapy was used for LCA before it was trialled on other retinal diseases that gradually reduce people’s vision as they grow older.
(b(i))[3]
Suggest how errors occurring during PCR can produce base substitution mutations in the DNA sequence of AAV.
(b(ii))[2]
Explain why the photoreceptor cells of the mouse fluoresced in step 3.
(b(iii))[1]
Predict the impact of the 7m8 AAV on treatment for age-related retinal diseases.
Worked solution & mark scheme
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