Describe how a gene is inserted into a bacterial plasmid to produce a recombinant plasmid during genetic modification.

Cambridge International IGCSE Biology (0610) — 21.3 Genetic modification · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Restriction enzymes cut the donor DNA to isolate the desired gene.
2. The same enzymes cut the bacterial plasmid, producing complementary sticky ends.
3. The gene is inserted into the plasmid; the sticky ends of gene and plasmid base‑pair.
4. DNA ligase seals the nicks, joining the ends to form a recombinant plasmid.

Examiner tips

Use the exact sequence of steps; include restriction enzymes, sticky ends, base‑pairing, and ligase.
Show the process in a clear, numbered list to match the mark scheme.
Mention that the same enzymes are used for both DNA fragments.

Common mistakes

Omitting the role of DNA ligase.
Confusing blunt ends with sticky ends.
Failing to state that the same restriction enzymes are used for both DNA fragments.

Mark scheme (4 marks)

Restriction enzymes are used to cut/isolate the desired gene from the donor organism's DNA
The same restriction enzymes are used to cut the bacterial plasmid, leaving complementary sticky ends
The gene is inserted into the plasmid, with the complementary sticky ends joining/base-pairing
DNA ligase joins the sticky ends to form the recombinant plasmid

Key terms in this question

plasmid · recombinant plasmid