The big idea: A clone is an organism (or cell) that is genetically identical to the one it came from.
Clones are made by asexual reproduction — a single parent makes offspring without gametes (sex cells) and without fertilisation.
Because asexual reproduction copies the parent's DNA by mitosis, every offspring carries the same genes as the parent. No new gene combinations are made, so there is no genetic variation among the clones.
- Clone
- An organism or cell that is genetically identical to another (it has the same DNA).
- Asexual reproduction
- Reproduction from a single parent, without gametes or fertilisation, producing offspring that are genetically identical to the parent.
- Mitosis
- Cell division that produces two genetically identical cells; it is how a parent's DNA is copied into clones.
- Vegetative propagation
- A form of asexual reproduction in plants where a new plant grows from a part of the parent plant (such as a stem cutting, runner or tuber).
- Somatic (body) cell
- Any cell of the body that is not a gamete — for example a skin or udder cell. Its nucleus carries the organism's full genetic information.
Why clones are identical: Asexual reproduction uses mitosis, which makes exact copies of the parent's DNA.
There is no meiosis and no fertilisation, so the gene combinations of the parent are passed on unchanged — every clone is genetically the same as the parent and as each other.
Some organisms clone themselves naturally, as their normal way of reproducing.
Humans also clone organisms artificially, on purpose — for example to grow many identical crop plants, or to copy a valuable animal.
All of these methods rely on mitosis, so in every case the offspring are genetically identical to the parent.
Natural cloning — budding and plant offshoots: Budding: in yeast (and in animals like Hydra), a small outgrowth — a bud — forms on the parent. It receives a copy of the genetic material and then pinches off as a smaller, genetically identical daughter cell or organism.
Plant offshoots: many plants grow new individuals from runners (strawberry), tubers (potato) or bulbs. Each new plant is a clone of the parent.
Artificial cloning — cuttings and tissue culture: Vegetative propagation (stem cuttings): a gardener cuts a stem from a parent plant, encourages it to grow roots, and raises a new plant that is genetically identical to the parent. This is the recommended way to clone a plant cheaply at home.
Tissue culture (micropropagation): a few cells from one plant are grown on a sterile nutrient medium into many identical plantlets — used to mass-produce crops such as bananas and orchids.
Cloning an adult animal — SCNT (Dolly the sheep): Cloning a whole adult animal is much harder. The method that succeeded is somatic-cell nuclear transfer (SCNT), used to make Dolly the sheep — the first cloned adult mammal.
The idea is simple: take the nucleus of an adult body cell (which holds the full set of genes) and put it into an egg cell whose own nucleus has been removed. The egg then develops into a clone of the nucleus donor.
Somatic-cell nuclear transfer — step by step
- Take a body (somatic) cell from the adult animal you want to clone, and remove its nucleus (this nucleus carries the full set of genetic information).
- Take an unfertilised egg cell from a donor and remove (enucleate) its own nucleus, leaving an empty egg.
- Insert the body-cell nucleus into the empty egg, so the egg now contains the donor animal's genetic information.
- Stimulate the egg to divide (for example with a small electric shock) so it develops into an early embryo.
- Implant the embryo into a surrogate mother, where it develops into an animal that is a genetic clone of the original nucleus donor.
Natural cloning
- Happens on its own, as normal reproduction
- Budding in yeast and Hydra
- Runners, tubers, bulbs in plants
- Offspring genetically identical to the parent
Artificial cloning
- Done deliberately by humans
- Stem cuttings and tissue culture in plants
- SCNT to clone an adult animal (Dolly)
- Offspring genetically identical to the parent / donor
The thread running through all of them: Whether natural or artificial, every cloning method copies the parent's DNA by mitosis.
So the answer to 'how similar are the clones?' is always the same: genetically identical, with no variation among them.
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How this is tested: On Paper 2 a 3-mark Outline question often asks you to outline one method that has successfully cloned an adult animal — the expected answer is somatic-cell nuclear transfer, described as a short sequence of steps.
On Paper 1 a 1-mark question may ask you to identify the recommended procedure for cloning plants from stem cuttings (vegetative propagation).
A Paper 1B data question can give an unfamiliar organism (such as yeast) and ask you to describe how it reproduces — the answer is budding — and then to deduce that the offspring are genetically identical.
IB-style question — outline how an adult animal is cloned
A prize dairy cow is to be cloned so that a genetically identical calf can be produced. Outline one method that could successfully clone this adult animal. [3]
How to score all three marks
- Name the method and get the nucleus. Use somatic-cell nuclear transfer: take a body (somatic) cell from the adult cow and remove its nucleus, which carries the cow's full genetic information.
- Prepare an empty egg and transfer the nucleus. Take an egg cell from a donor and remove its own nucleus, then insert the body-cell nucleus into this empty egg so it now contains the prize cow's genes.
- Grow and implant the embryo. Stimulate the egg to divide into an embryo and implant it into a surrogate mother, where it develops into a calf that is a genetic clone of the original cow. (Mark 1: somatic nucleus removed. Mark 2: placed into an enucleated egg. Mark 3: embryo stimulated and implanted to grow a clone.)
Final answer
Somatic-cell nuclear transfer: remove the nucleus from a body cell of the cow; remove the nucleus from a donor egg; insert the body-cell nucleus into the empty egg; stimulate it to form an embryo; implant the embryo into a surrogate mother to grow a genetically identical calf.
✓ Why this scores full marks: It is a clear sequence of distinct steps: get the body-cell nucleus → put it into an enucleated egg → grow and implant the embryo.
An 'outline' worth 3 marks needs three separate scoring points, not the single phrase 'they cloned it'.
| Cloning method | Natural or artificial? | What happens | Example organism |
|---|---|---|---|
| Budding | Natural | A small outgrowth (bud) forms on the parent, receives a copy of the genetic material, then detaches as a smaller identical individual | Yeast, Hydra |
| Runners / tubers / bulbs | Natural | A parent plant grows new stems or storage organs that develop into separate, genetically identical plants | Strawberry (runners), potato (tubers) |
| Vegetative propagation (cuttings) | Artificial | A gardener takes a stem cutting, encourages it to grow roots, and raises a new plant identical to the parent | Many garden and crop plants |
| Tissue culture (micropropagation) | Artificial | A few cells from one plant are grown on a sterile nutrient medium into many identical plantlets | Orchids, banana, commercial crops |
| Somatic-cell nuclear transfer (SCNT) | Artificial | A body-cell nucleus is placed into an egg whose own nucleus has been removed; the egg is stimulated to divide and implanted | Dolly the sheep (first cloned adult mammal) |