A scientist cuts a circular plasmid once with a restriction enzyme. A gene fragment has two complementary sticky ends and is mixed with the cut plasmid and ligase.
Why must the resulting plasmids be checked for the required gene?
Some plasmids may close again without incorporating the gene fragment.
Restriction enzymes may insert the gene when they reopen the original plasmid.
Ligase may join matching ends only when a complete donor gene lies between them.
Complementary ends may guarantee insertion before any DNA is joined by ligase.
44 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.