19. Genetic technology
A section of Biology, 9700
Listing 10 of 107 questions
Gene therapy can be used to treat some genetic disorders. An appropriate vector is chosen to carry the normal allele into the target cell. Three types of vectors commonly chosen are naked DNA, viruses and liposomes. A trial of gene therapy to treat cystic fibrosis used a viral vector. The viral vector caused a primary immune response with the production of memory cells. Explain why the production of memory cells prevents the gene therapy from working in long-term chronic conditions such as cystic fibrosis. With reference to the three types of vectors that are commonly used, discuss the challenges in choosing appropriate vectors for use in gene therapy. Do not include problems associated with an immune response in your answer. A trial was carried out to find a new vector for use in gene therapy. The new vector was made from red blood cells taken from the person with the genetic disorder. The cells had most of their cytoplasmic content removed and were then broken up to make small spherical vectors. Most of these vectors lacked the ability to bind to receptors on the target cells. To solve this problem, genetically engineered stem cells taken from the person were used to form red blood cells. These red blood cells had membrane proteins that were complementary to the target cell receptors. The vectors that were produced were well-tolerated by the immune system. Explain why the vectors were well-tolerated by the immune system. Suggest why it is not possible to produce genetically engineered red blood cells, except by using genetically engineered stem cells.
9700_s20_qp_42
THEORY
2020
Paper 4, Variant 2
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Insulin can be produced on a large scale using gene technology and prokaryotes such as Escherichia coli. Table 7.1 summarises the sequence of steps in one method of production of insulin by E. coli. Complete Table 7.1 by adding one statement in each of the empty boxes. Table 7.1 step reason for step obtain copies of gene with sticky ends the gene codes for the synthesis of insulin acts as a vector for the transfer of the gene into the host use restriction endonuclease enzyme mix vector and gene to seal the sugar-phosphate backbone to obtain transformed host E. coli cells screen for, and obtain, successfully transformed cells to obtain large amounts of insulin for extraction and purification
9700_w11_qp_41
THEORY
2011
Paper 4, Variant 1
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Insulin can be produced on a large scale using gene technology and prokaryotes such as Escherichia coli. Table 7.1 summarises the sequence of steps in one method of production of insulin by E. coli. Complete Table 7.1 by adding one statement in each of the empty boxes. Table 7.1 step reason for step obtain copies of gene with sticky ends the gene codes for the synthesis of insulin acts as a vector for the transfer of the gene into the host use restriction endonuclease enzyme mix vector and gene to seal the sugar-phosphate backbone to obtain transformed host E. coli cells screen for, and obtain, successfully transformed cells to obtain large amounts of insulin for extraction and purification
9700_w11_qp_42
THEORY
2011
Paper 4, Variant 2
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There are many different strains of the soil bacterium Bacillus thuringiensis. Each produces slightly different types of Cry-proteins, which are toxic to insects. Some types of cotton, known as Bt cotton, have been genetically modified to produce one of these proteins, Cry1Ac. This protein acts specifically to kill the larvae of butterflies and moths, including the cotton bollworm, Helicoverpa zea, a serious pest of cotton crops. The genetically modified cotton contains a ‘genetic package’ that includes: • the gene coding for Cry1Ac, the Bt protein • a promoter • a herbicide resistance gene that is used as a marker. Suggest the advantages of using, in Bt cotton, the gene coding for Cry1Ac, rather than one of the genes coding for other types of the Cry-protein. Explain why a promoter is included in the genetic package. Suggest how the herbicide resistance gene can be used as a genetic marker. Table 4.1 shows information about the cultivation of Bt cotton and non-GM cotton by farmers in India in 2002–2003. Table 4.1 Bt cotton non-GM cotton mean yield of cotton / kg ha–1 seed cost / rupees ha–1 insecticide cost / rupees ha–1 net income / rupees ha–1 With reference to Table 4.1, compare the costs involved in growing Bt cotton with the costs involved in growing non-GM cotton. Table 4.1 shows that farmers who grow Bt cotton have a higher net income than those who grow non-GM cotton. Use the information in the table to suggest one reason why some farmers in India choose to grow non-GM cotton, rather than Bt cotton. In one region of India, Andhra Pradesh, a severe drought in 2002–2003 meant that Bt cotton grew less well than other varieties of cotton that were better adapted for the conditions. Suggest how a variety of Bt cotton that is better adapted to dry conditions could be produced from the existing varieties of Bt cotton, without using gene technology.
9700_w17_qp_41
THEORY
2017
Paper 4, Variant 1
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There are many different strains of the soil bacterium Bacillus thuringiensis. Each produces slightly different types of Cry-proteins, which are toxic to insects. Some types of cotton, known as Bt cotton, have been genetically modified to produce one of these proteins, Cry1Ac. This protein acts specifically to kill the larvae of butterflies and moths, including the cotton bollworm, Helicoverpa zea, a serious pest of cotton crops. The genetically modified cotton contains a ‘genetic package’ that includes: • the gene coding for Cry1Ac, the Bt protein • a promoter • a herbicide resistance gene that is used as a marker. Suggest the advantages of using, in Bt cotton, the gene coding for Cry1Ac, rather than one of the genes coding for other types of the Cry-protein. Explain why a promoter is included in the genetic package. Suggest how the herbicide resistance gene can be used as a genetic marker. Table 4.1 shows information about the cultivation of Bt cotton and non-GM cotton by farmers in India in 2002–2003. Table 4.1 Bt cotton non-GM cotton mean yield of cotton / kg ha–1 seed cost / rupees ha–1 insecticide cost / rupees ha–1 net income / rupees ha–1 With reference to Table 4.1, compare the costs involved in growing Bt cotton with the costs involved in growing non-GM cotton. Table 4.1 shows that farmers who grow Bt cotton have a higher net income than those who grow non-GM cotton. Use the information in the table to suggest one reason why some farmers in India choose to grow non-GM cotton, rather than Bt cotton. In one region of India, Andhra Pradesh, a severe drought in 2002–2003 meant that Bt cotton grew less well than other varieties of cotton that were better adapted for the conditions. Suggest how a variety of Bt cotton that is better adapted to dry conditions could be produced from the existing varieties of Bt cotton, without using gene technology.
9700_w17_qp_43
THEORY
2017
Paper 4, Variant 3
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Haemophilia is a blood clotting disorder in humans caused by a mutant allele on the X chromosome. Table 4.1 compares two forms of haemophilia: haemophilia A and haemophilia B. Table 4.1 haemophilia A haemophilia B gene F8 F9 clotting factor protein factor VIII factor IX proportion of males born with haemophilia 1 in 5000 1 in 30 000 length of functional gene (exons only) / kilobase pairs 7.0 1.6 Genetic engineering is used to make recombinant human proteins to treat people with haemophilia A and haemophilia B. Outline the principles of genetic engineering. Scientists are working towards a goal of treating haemophilia by gene therapy. They plan to use a common, harmless virus to introduce the functional gene. The virus has a genome that is 4.7 kilobase pairs long. With reference to Table 4.1 and the introduction to , assess: • which form of haemophilia, A or B, scientists should try to treat first • whether they should attempt to treat haemophilia with gene therapy at all. Explain your reasoning. In gene therapy trials to treat haemophilia, the gene coding for the clotting factor needs to be introduced together with a promoter. Explain why a promoter has to be introduced as well as the desired gene. Some individuals taking part in gene therapy trials have been naturally exposed to the virus carrying the functional gene, so that their blood already contains antibodies to the virus. Predict how this will affect the success of the gene therapy treatment. Gene editing is a newer technique for modifying DNA. Some scientists are researching the use of gene editing, instead of introducing a functional gene, to treat haemophilia. State two possible advantages of using gene editing as a method of treating haemophilia.
9700_w22_qp_42
THEORY
2022
Paper 4, Variant 2
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Questions Discovered
107