A farmer wants to produce a large number of genetically identical prize-winning cattle quickly. Explain how embryo transplantation could be used to achieve this, and why the offspring produced would be genetically identical to each other.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Prize-winning cattle have been selectively bred for decades to produce high-quality meat. A farmer discovers that one of his best cows has an exceptionally desirable genotype and wants to produce as many offspring with that genotype as possible in a short time.
Model answer (5 marks)
1. The prize cow is treated with hormones to super‑ovulate, producing many eggs.
2. The eggs are fertilised by sperm from a prize bull (artificial insemination or in‑vitro fertilisation).
3. The resulting embryos are collected before they develop beyond the early stage.
4. Each embryo is transplanted into the uterus of a surrogate cow to carry to term.
5. All offspring are genetically identical because they all contain the same DNA from the donor cow and bull, i.e. they are clones of the original genotype.
2. The eggs are fertilised by sperm from a prize bull (artificial insemination or in‑vitro fertilisation).
3. The resulting embryos are collected before they develop beyond the early stage.
4. Each embryo is transplanted into the uterus of a surrogate cow to carry to term.
5. All offspring are genetically identical because they all contain the same DNA from the donor cow and bull, i.e. they are clones of the original genotype.
Examiner tips
- Use the sequence of steps: super‑ovulation, fertilisation, embryo collection, transplantation, genetic identity. Show that all embryos come from the same donor and bull. Mention ‘clones’ or ‘genetically identical’ to hit the mark.
- common_mistakes
- :
- Confusing super‑ovulation with natural ovulation. Forgetting to state that all embryos come from the same donor. Using vague terms like ‘many cows’ instead of ‘surrogate uterus’.
Mark scheme (5 marks)
- The prize cow (donor) is given hormones to stimulate her to produce many eggs / superovulation
- The eggs are fertilised by sperm from a prize bull (artificially inseminated / fertilised in the laboratory)
- The embryos are removed / collected before they are allowed to develop significantly
- Each embryo is transplanted into a surrogate / host cow's uterus to develop to term
- The offspring are genetically identical to each other because they all contain the same DNA / genotype inherited from the same donor cow and bull / they all developed from embryos with the same genetic material
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →