Gene technology: exam questions

Answer: B (1) Restriction enzymes cut; ligase joins by phosphodiester bonds.

• cut the gene and plasmid with the same restriction endonuclease (1)
• at its recognition site / specific base sequence (1)
• staggered cut leaves complementary sticky ends (1)
• gene and plasmid mixed so sticky ends join by complementary base pairing / hydrogen bonds (1)
• DNA ligase joins the sugar–phosphate backbones / forms phosphodiester bonds (1)
• Max 5

• beta cells make large amounts of insulin mRNA (1)
• reverse transcriptase makes a cDNA copy of the mRNA (1)
• cDNA has no introns, which bacteria cannot remove, so the gene can be expressed in bacteria (1)

• bacteria spread on agar containing the antibiotic (1)
• bacteria with the plasmid have (and express) the resistance gene (1)
• so they survive and grow into colonies (1)
• bacteria without the plasmid are killed / do not grow (1)
• colonies are picked off / subcultured to grow a culture of transformed bacteria (1)
• Max 4. Ignore description of how the plasmid was inserted (calcium chloride, heat shock)

• insulin is identical to human insulin / gene is the human gene, so less chance of an immune response (1)
• bacteria reproduce quickly / large amounts can be made in fermenters (1)
• cheaper / reliable supply (1)
• fewer ethical objections as animals are not killed (1)
• Max 4

• mRNA extracted from the cells and converted to labelled (fluorescent) cDNA (1)
• cDNA binds to complementary DNA probes on the array (1)
• spots that fluoresce show the gene is active / brighter spot means more mRNA (1)
• (b) use of computer science / software to store, analyse and interpret biological data (e.g. DNA sequences) (1)

• (a) gene inserted into the Ti plasmid of Agrobacterium / DNA coated onto gold or tungsten particles (1)
• (a) Agrobacterium infects plant cells and transfers the gene into the plant genome / particles fired into plant cells with a gene gun (1)
• (b) gene microinjected into the nucleus of a fertilised egg (1)
• (b) embryo implanted into a surrogate mother, which gives birth to a transgenic animal (1)
• Max 3. At least one mark from each part for full marks

• benefit: reduces vitamin A deficiency / improves nutrition in people with a rice-based diet (1)
• benefit: higher yield / pest-resistant crops / less pesticide, so greater food security (1)
• risk: gene transfer by pollen to wild relatives / weeds (1)
• risk: harm to non-target organisms / reduced biodiversity (1)
• risk: unforeseen health effects / allergies; long-term effects not fully known (1)
• economic / ethical: seeds patented and costly for farmers; some object to modifying organisms (1)
• reasoned judgement that weighs benefits against risks / suggests monitoring and testing (1)
• Max 6