Question
What is animal cloning? Describe the process used to create Dolly the sheep. Compare reproductive cloning with therapeutic cloning. What ethical concerns surround each type?
(NEET + CBSE Board pattern — process + comparison)
Solution — Step by Step
The process involved three sheep:
- Finn Dorset ewe — Mammary cell was taken. The nucleus (diploid, 2n) was isolated.
- Scottish Blackface ewe — An oocyte (egg cell) was taken. Its nucleus was removed (enucleation).
- The Finn Dorset nucleus was inserted into the enucleated Scottish Blackface egg cell.
- The reconstructed cell was given an electric pulse to stimulate fusion and division.
- The embryo was implanted into a third surrogate mother (another Scottish Blackface ewe).
- Dolly was born on July 5, 1996 — genetically identical to the Finn Dorset ewe (mammary cell donor).
Dolly proved that a differentiated somatic cell could be reprogrammed to produce an entire organism — a revolutionary finding.
| Feature | Reproductive Cloning | Therapeutic Cloning |
|---|---|---|
| Goal | Produce a genetically identical organism | Produce embryonic stem cells for medical treatment |
| Process | SCNT → embryo → implant in uterus → birth | SCNT → embryo → harvest stem cells (embryo destroyed) |
| Embryo fate | Develops into a full organism | Destroyed at blastocyst stage |
| Application | Animal breeding, endangered species | Tissue repair, organ regeneration, disease research |
| Example | Dolly the sheep | Stem cell therapy for Parkinson’s, diabetes |
| Ethical concern | Playing God, abnormalities in clones | Destruction of embryo = destruction of potential life |
- Dolly’s nuclear DNA came from the mammary cell donor (Finn Dorset)
- Dolly’s mitochondrial DNA came from the enucleated egg donor (Scottish Blackface) — because mitochondria are in the cytoplasm, not the nucleus
- Dolly showed signs of premature ageing (arthritis, shortened telomeres) — suggesting that the donor cell’s age affected the clone
- Dolly was euthanised in 2003 due to progressive lung disease
graph TD
A["Finn Dorset Ewe"] -->|"Mammary cell nucleus"| D["Reconstructed Cell"]
B["Scottish Blackface Ewe"] -->|"Enucleated egg"| D
D -->|"Electric pulse"| E["Embryo develops"]
E --> F{"Purpose?"}
F -->|Reproductive| G["Implant in surrogate → Dolly born"]
F -->|Therapeutic| H["Harvest stem cells at blastocyst"]
style A fill:#f9a8d4,stroke:#000
style B fill:#93c5fd,stroke:#000
style G fill:#86efac,stroke:#000,stroke-width:2pxWhy This Works
Dolly demonstrated that cell differentiation is reversible. Every cell in the body carries the complete genome — mammary cells, skin cells, liver cells all have the same DNA. What makes them different is which genes are expressed. The egg cell cytoplasm contains factors that can “reset” a somatic cell nucleus to a totipotent state, allowing it to develop into a complete organism.
This concept — nuclear reprogramming — is the foundation of both reproductive and therapeutic cloning.
Common Mistake
The classic error: students write that Dolly was genetically IDENTICAL to the Scottish Blackface ewe (egg donor). This is wrong. Dolly’s nuclear DNA came from the Finn Dorset mammary cell. The Scottish Blackface only provided the enucleated egg (cytoplasm + mitochondrial DNA). NEET specifically tests which sheep Dolly was a clone of — the answer is Finn Dorset.
Remember: “3 mothers of Dolly” — mammary cell donor (genetic mother), egg donor (cytoplasmic mother), and surrogate mother (gestational mother). This three-mother concept is unique to SCNT cloning and appears in NEET questions regularly.