Scientists have developed a genetically engineered goat that produces a human protein called antithrombin in its milk. Antithrombin is used to treat patients whose blood clots dangerously. Explain how genetic engineering could be used to produce a goat that makes human antithrombin in its milk.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Antithrombin is a human protein that prevents dangerous blood clotting. It is normally produced in human liver cells. Scientists wanted to produce large quantities of antithrombin cheaply, so they genetically engineered goats to secrete the protein in their milk.
Model answer (5 marks)
1. The human gene that codes for antithrombin is isolated from human DNA.
2. A suitable vector, such as a plasmid, is constructed to carry the antithrombin gene.
3. The plasmid is introduced into a goat embryo cell or fertilised egg cell at an early developmental stage.
4. The antithrombin gene becomes incorporated into the goat’s genome and is stably integrated into the DNA.
5. The transgenic goat expresses the human antithrombin gene and secretes the protein into its milk, which can then be collected for use.
2. A suitable vector, such as a plasmid, is constructed to carry the antithrombin gene.
3. The plasmid is introduced into a goat embryo cell or fertilised egg cell at an early developmental stage.
4. The antithrombin gene becomes incorporated into the goat’s genome and is stably integrated into the DNA.
5. The transgenic goat expresses the human antithrombin gene and secretes the protein into its milk, which can then be collected for use.
Examiner tips
- Use the exact sequence of steps: isolate gene → vector construction → introduction into embryo → integration → expression in milk.
- Show the gene is human and the vector is a plasmid; mention early-stage embryo to ensure germline transmission.
- Mention that the protein is secreted into milk, not just produced.
Mark scheme (5 marks)
- The human gene that codes for antithrombin is identified and cut out / isolated from human DNA
- A vector (such as a plasmid) is used to carry the human gene
- The vector / gene is introduced into a goat embryo cell / fertilised egg cell at an early stage
- The human gene becomes part of the goat's genome / is incorporated into the goat's DNA
- The goat expresses the human gene and produces / secretes antithrombin in its milk, which can then be collected
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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