19. Genetic technology
A section of Biology, 9700
Listing 10 of 107 questions
In 1973, a technique for genetic engineering was used for the first time. Recombinant DNA was made using a plasmid and this was successfully transferred into an organism. In 2012, a new technique for genetic engineering, called gene editing, was developed. Table 4.1 lists some statements about the two genetic engineering techniques. Complete Table 4.1 to compare the original genetic engineering technique using a plasmid vector with the newer technique of gene editing. For each row, place a tick (3) in the correct column if the statement applies and leave a blank if the statement does not apply. Table 4.1 statement genetic engineering using a plasmid gene editing It may cause the organism to produce a different protein. It may cause a single base pair in a gene to be changed. The success of the technique can be evaluated using marker genes. It may use the CRISPR system. It uses DNA ligase. Cassava plants, Manihot esculenta, produce roots that have a high starch content. These roots are an important food source in tropical regions. The growth of cassava plants is reduced by competition from weeds. Scientists used gene editing to develop two types of cassava plant with different mutations (changes to the DNA). The gene edited cassava plants showed resistance to the herbicide glyphosate. In susceptible plants, glyphosate prevents synthesis of three amino acids from a precursor molecule called shikimate. shows the concentration of shikimate in the wild type (not gene edited) and the two types of gene edited cassava plant after they were exposed to three different concentrations of glyphosate. shikimate concentration / arbitrary units type of cassava plant Key: glyphosate / μmol dm–3 A B C Identify the letter in that represents the wild type cassava plant. Explain the social benefit of this example of gene editing.
9700_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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In 1973, a technique for genetic engineering was used for the first time. Recombinant DNA was made using a plasmid and this was successfully transferred into an organism. In 2012, a new technique for genetic engineering, called gene editing, was developed. Table 4.1 lists some statements about the two genetic engineering techniques. Complete Table 4.1 to compare the original genetic engineering technique using a plasmid vector with the newer technique of gene editing. For each row, place a tick (3) in the correct column if the statement applies and leave a blank if the statement does not apply. Table 4.1 statement genetic engineering using a plasmid gene editing It can add a new phenotypic characteristic to an organism. It can change an A–T base pair to C–G. It can inactivate a desired selected gene in an organism. It may change DNA in a way that cannot be distinguished from a natural mutation. It requires a DNA donor and a recipient. Camelina sativa is a fast-growing plant with oil-rich seeds. C. sativa grows in dry and poor soils and so it may be important as a food crop in the future. The oil from its seeds has a high content of polyunsaturated fatty acids. This shortens the time that the oil can be stored for, which is a disadvantage. Scientists used gene editing to develop two types of C. sativa with different genetic changes. The gene edited C. sativa seeds produced oil with longer storage times. shows the percentage composition of fatty acids in the oil extracted from seeds of gene edited and wild type (not gene edited) C. sativa. 16:0 18:0 18:1 18:2 fatty acids shown as number of carbons:number of C=C double bonds percentage composition of fatty acids 18:3 20:1 22:1 type A type B type C Key Identify the letter that represents the oil of the wild type C. sativa on . With reference to , discuss the social benefits of this example of gene editing.
9700_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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Green fluorescent protein (GFP) is a small protein that emits bright green fluorescence in blue light. It was first isolated from the jellyfish, Aequorea victoria. The gene coding for GFP can be expressed in bacteria, such as Escherichia coli, and so it is often used as a marker to show successful uptake of a gene by the bacterium. Outline how a gene from another species can be inserted into E. coli. Explain how a marker gene, such as the gene for GFP, is used to show successful uptake of a gene for a wanted protein. Genes for enzymes that produce fluorescent substances are often used as markers in gene technology. GFP is not an enzyme. Suggest one disadvantage of using the gene for GFP to produce easily detectable fluorescence, rather than using a gene for an enzyme that produces a fluorescent substance. Explain your answer. disadvantage explanation
9700_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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Green fluorescent protein (GFP) is a small protein that emits bright green fluorescence in blue light. It was first isolated from the jellyfish, Aequorea victoria. The gene coding for GFP can be expressed in bacteria, such as Escherichia coli, and so it is often used as a marker to show successful uptake of a gene by the bacterium. Outline how a gene from another species can be inserted into E. coli. Explain how a marker gene, such as the gene for GFP, is used to show successful uptake of a gene for a wanted protein. Genes for enzymes that produce fluorescent substances are often used as markers in gene technology. GFP is not an enzyme. Suggest one disadvantage of using the gene for GFP to produce easily detectable fluorescence, rather than using a gene for an enzyme that produces a fluorescent substance. Explain your answer. disadvantage explanation
9700_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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Traditional techniques for genetically modifying organisms use three enzymes: • restriction endonuclease • reverse transcriptase • DNA ligase. For example, these enzymes have been used to produce genetically modified pigs containing the GFP gene coding for green fluorescent protein, originally sourced from jellyfish. Outline how these three enzymes could be used in genetically engineering a transgenic pig containing the GFP gene. A new technique that aims to cause a deletion in a gene uses an enzyme called Cas9 nuclease. It is injected into zygotes along with an RNA sequence (the guide RNA) that is complementary to a target gene. The Cas9 nuclease causes a deletion in the target gene in the zygotes, preventing the expression of that gene. The toxicity and efficiency of the new technique was tested on four groups of pig zygotes. These pig zygotes were produced by IVF using: • ova from a female non-transgenic pig. • sperm from a male transgenic pig whose somatic cells contained one copy of the GFP gene per cell. The pig zygotes in three groups were injected with different concentrations of Cas9 nuclease and guide RNA targeted at the GFP gene. The fourth group of pig zygotes (control group) was not injected with Cas9 nuclease and guide RNA. Explain why the GFP gene was chosen for testing the new technique. Some of the zygotes in each group survived and after six days each had developed into a group of cells called a blastocyst. The blastocysts were counted using a light microscope. A filter was then added to the microscope, so that only blastocysts expressing the green fluorescent protein showed up. These were counted and the results are summarised in Table 5.1. Table 5.1 concentration of Cas9 nuclease and guide RNA / ng mm–3 number of blastocysts seen under white light number of blastocysts seen under filter 0 68 Calculate the percentage of zygotes in the control group that were transgenic. Show your working. % Explain whether the percentage you calculated for is higher or lower than expected. Name a statistical test that would allow you to test the significance of the difference between the percentage you calculated in and the expected percentage. State the best concentration of Cas9 nuclease and guide RNA to use to cause a deletion in the GFP gene and give reasons for your choice. shows the results from a second trial of the new technique, analysed by electrophoresis. • Lanes 1–4 show DNA from four pigs born after Cas9 nuclease was used to cause a deletion in a target gene coding for a cell surface protein. • Lane 5 shows DNA from their surrogate mother. • Lane 6 shows DNA from another normal pig for comparison. The size of the DNA fragments is given in kilobase pairs as shown in . 1 kbp is 1000 base pairs of DNA. The target gene measures 6 kbp and codes for a cell surface protein that is essential for the disease virus PRRSV to infect cells in the pig’s body. 6 kbp 4 kbp Explain what indicates about the success of the new technique in causing a deletion in a gene in pigs so that they show resistance to PRRSV.
9700_w18_qp_42
THEORY
2018
Paper 4, Variant 2
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Questions Discovered
107