A scientist wants to transfer a gene for salt tolerance from a bacterium into a crop plant. The required gene extends from base position 1400 to base position 2600 in the donor DNA. The plasmid must be opened by cutting it at one position only.
The table shows the positions where four restriction enzymes cut the donor DNA and a circular plasmid. For each row, the same enzyme would be used on the donor DNA and the plasmid, producing complementary sticky ends.
| Enzyme | Cut positions in donor DNA | Cut positions in circular plasmid |
|---|---|---|
| A | 1200 and 2800 | 900 |
| B | 1200, 2000 and 2800 | 900 |
| C | 1300 and 2700 | 900 and 3300 |
| D | 1500 and 2500 | 900 |
Explain which enzyme the scientist should use. In your answer, calculate the length of the donor DNA fragment produced and predict what would happen if DNA ligase were not added after the sticky ends had paired.
100 exam-style questions on Edexcel GCSE Biology 4.3 Selective breeding and genetic modification, covering 4.3.1 Selective breeding and its impact, 4.3.2 Tissue culture, 4.3.3 Genetic engineering overview, 4.3.4 Main stages of genetic engineering, 4.3.5 Advantages and disadvantages of GM organisms, 4.3.6 Agricultural solutions for a growing population, and 4.3.7 Evaluating genetic engineering and breeding. Each one has a worked solution and a mark scheme showing where the marks go.