Gene technologyEdexcel A-Level Biology B: Subtopic test

1. 1
   Scientists want bacteria to make human insulin. They cut the human insulin gene out of human DNA and cut a bacterial plasmid with the same restriction endonuclease. The enzyme cuts at a specific recognition sequence and leaves short single-stranded overhangs at each end of the cut DNA.

   (a)

   Which enzyme cuts the insulin gene out of the human DNA?

   [1 mark]

   • ADNA ligase
   • BDNA polymerase
   • CHelicase
   • DRestriction endonuclease

   (b)

   Which enzyme forms the covalent bonds that join the insulin gene to the plasmid once the overhangs have paired up?

   [1 mark]

   • ADNA ligase
   • BRestriction endonuclease
   • CRNA polymerase
   • DDNA helicase

   (c)

   Explain why the same restriction endonuclease is used to cut both the human DNA and the plasmid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A plasmid carries two antibiotic resistance genes, one for ampicillin and one for tetracycline. A human gene is inserted into the middle of the tetracycline resistance gene. Bacteria are mixed with the plasmids and spread on agar containing ampicillin (the master plate). Colonies are then transferred by pressing a sterile velvet pad first on the master plate and then on agar containing tetracycline (the replica plate), keeping the positions of the colonies.

   (a)

   Which colonies on the master plate contain bacteria with recombinant plasmids?

   [1 mark]

   • AColonies that also grow on the replica plate
   • BColonies that are on the master plate but not on the replica plate
   • CColonies that are on neither plate
   • DColonies that grow only on the replica plate

   (b)

   What is the purpose of replica plating?

   [1 mark]

   • ATo kill the bacteria that have taken up a plasmid
   • BTo insert the human gene into the plasmid
   • CTo copy the pattern of colonies so that colonies can be matched between the two plates
   • DTo increase the rate of mutation in the bacteria

   (c)

   Explain why bacteria containing a plasmid without the human gene grow on both plates.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Researchers have identified a human gene, called gene X, which they think is involved in the development of the heart. They produce knockout mice in which gene X has been inactivated in every cell and compare the mice with normal mice.

   (a)

   Explain how the knockout mice can be used to find out the function of gene X.

   [3 marks]

   (b)

   Suggest two limitations and one ethical issue of using knockout mice to investigate the function of human genes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company wants to improve soya beans. Natural soya oil is rich in polyunsaturated fatty acids, which are easily oxidised and make soya products go rancid. The company silenced the gene for the enzyme that converts oleic acid, a monounsaturated fatty acid, into polyunsaturated fatty acids. It also introduced a bacterial gene for tolerance of a weedkiller (herbicide). The new soya has attracted both support and protest.

   (a)

   Describe how a herbicide-tolerance gene could be introduced into soya cells, and explain how this improves soya production.

   [6 marks]

   (b)

   Evaluate the widespread use of genetically modified crops, such as this soya, and justify a conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions