What you'll learn
Cloning produces genetically identical organisms, and it is used in agriculture, conservation and research. For AQA GCSE Biology you need to understand what a clone is, the methods of cloning plants (cuttings and tissue culture) and animals (embryo transplants and adult cell cloning), and the benefits and concerns of cloning. This guide covers what cloning is, the plant and animal methods, and the advantages and disadvantages. By the end you should be able to describe each cloning method and evaluate the use of cloning.
Key terms and definitions
Clone — A genetically identical copy of an organism.
Asexual reproduction — Reproduction from one parent, producing genetically identical offspring.
Cutting — A piece of a plant that grows into a new, identical plant.
Tissue culture — Growing new plants from small groups of cells in the laboratory.
Embryo transplant — Splitting an embryo and implanting the identical parts into surrogate mothers.
Adult cell cloning — Making a clone from the nucleus of an adult body cell.
Nucleus — The part of a cell that contains the genetic material.
Surrogate — An animal that carries and gives birth to offspring it is not genetically related to.
Core concepts
What cloning is
A clone is a genetically identical copy of an organism. Cloning is a form of asexual reproduction, because the offspring come from one parent and are genetically identical to it (and to each other). Cloning happens naturally in some organisms, but it can also be done artificially, and there are different methods for plants and animals.
Cloning plants: cuttings
Plants are relatively easy to clone. The simplest method is taking cuttings: a gardener takes a small piece of a plant, such as a stem with a few leaves, and plants it so it grows roots and becomes a new plant. The new plant is genetically identical to the parent. This is a quick, cheap and simple way to produce many identical plants, and it has been used by gardeners for a long time.
Cloning plants: tissue culture
Tissue culture is a more modern method used to produce large numbers of identical plants from very small amounts of tissue. The steps are:
- Small groups of cells are taken from part of a plant.
- They are grown on a special growth medium containing nutrients and hormones, in sterile (aseptic) conditions.
- The cells grow and divide to form new plants, which are genetically identical to the parent.
Tissue culture is used to produce many plants quickly, to preserve rare plant species, and by growers to reproduce plants with desirable features. It needs more skill and equipment than cuttings but can produce far more plants from a tiny sample.
Cloning animals: embryo transplants
Animals are harder to clone than plants. One method is embryo transplants:
- Sperm from a good-quality male is used to fertilise an egg from a good-quality female.
- The resulting embryo is allowed to develop a little, then split into several smaller embryos before the cells become specialised.
- Each of these identical embryos is implanted into a surrogate mother, which carries and gives birth to it.
The offspring are all genetically identical to each other (but not to the surrogates). This lets farmers produce many offspring from their best animals.
Cloning animals: adult cell cloning
Adult cell cloning produces a clone of an existing adult animal. The steps are:
- The nucleus is removed from an egg cell (which is left with no nucleus).
- The nucleus from an adult body cell of the animal to be cloned is inserted into the empty egg cell.
- The egg is given a small electric shock, which makes it divide to form an embryo.
- The embryo is implanted into a surrogate mother, which gives birth to a clone of the animal that supplied the adult cell.
This is the method famously used to clone Dolly the sheep. The clone is genetically identical to the animal that provided the body-cell nucleus.
Benefits and concerns of cloning
Cloning has clear benefits: it can quickly produce many organisms with desirable characteristics (such as high-yield crops or productive farm animals), help preserve endangered species, and produce identical animals for research. However, there are concerns: cloned populations have very little genetic variation, which makes them more vulnerable to disease or environmental change; adult cell cloning is difficult, expensive and often unsuccessful; and there are ethical concerns about cloning animals and about welfare. Because there are strong points on both sides, cloning is often set as an "evaluate" question.
Cloning and genetic variation
A key idea running through cloning is its effect on genetic variation. Because clones are genetically identical, cloning produces no new variation — unlike sexual reproduction, which mixes alleles from two parents to produce varied offspring. This has advantages: a grower can reliably reproduce a plant or animal with exactly the desired features. But it also has a serious drawback: a population of clones is genetically uniform, so if a disease or environmental change affects one individual, it can affect them all. This lack of variation reduces the population's ability to adapt, which is why relying heavily on clones can be risky. Linking cloning back to variation and its importance for survival shows a deeper understanding.
Uses of cloning in medicine and research
Cloning also has important applications in medicine and research. Cloning animals allows scientists to produce genetically identical individuals for experiments, so that results are not affected by genetic differences between the animals. Cloned animals can also be engineered to produce useful substances, such as medicines in their milk. There is also research into using cloning techniques to produce cells or tissues for treating human diseases, for example to replace damaged cells. These uses are promising but raise ethical questions, which is why cloning remains a topic of debate. Being able to mention both the potential benefits and the concerns gives a balanced answer.
Worked examples
Example 1: Why a cutting is a clone
Explain why a plant grown from a cutting is a clone of the parent. The cutting is a piece of the parent plant, so it grows using cells that are genetically identical to the parent. This is asexual reproduction from one parent, so the new plant has the same genes as the parent and is a clone.
Example 2: Describing adult cell cloning
Describe the main steps of adult cell cloning. The nucleus is removed from an egg cell. The nucleus of an adult body cell from the animal to be cloned is inserted into the empty egg. An electric shock makes the egg divide into an embryo, which is implanted into a surrogate mother that gives birth to a clone.
Example 3: Advantage of tissue culture
Give one advantage of tissue culture over taking cuttings. Tissue culture can produce a very large number of identical plants from a tiny sample of tissue, and can be used to preserve rare species, whereas cuttings produce fewer plants and need larger pieces of the parent plant.
Example 4: A concern about cloning
Explain one disadvantage of producing a population of cloned animals. Cloned animals are genetically identical, so the population has very little genetic variation. This makes them all vulnerable to the same diseases or environmental changes, so a single disease could affect the whole population.
Common mistakes and how to avoid them
A common error is muddling embryo transplants and adult cell cloning. In embryo transplants, an embryo is split into identical parts; in adult cell cloning, an adult cell nucleus is put into an empty egg. Learn the steps of each separately.
Students often forget that the clone in adult cell cloning is identical to the animal that provided the body cell nucleus, not to the egg donor or the surrogate. The nucleus carries the genes.
Another mistake is thinking cloning always produces variation. Clones are genetically identical, so cloning reduces variation — this lack of variation is one of the main concerns.
When describing tissue culture, remember it must be done in sterile (aseptic) conditions on a medium with nutrients and hormones. Leaving out the sterile conditions loses marks.
Finally, for evaluation questions, give both benefits and concerns. Cloning can produce many useful organisms but reduces variation and raises ethical and welfare issues.
Exam technique for "Cloning"
Be ready to describe each method in the correct order: cuttings, tissue culture, embryo transplants and adult cell cloning. The steps of adult cell cloning (remove egg nucleus, insert adult cell nucleus, electric shock, implant in surrogate) are especially commonly tested.
Distinguish the plant methods (cuttings, tissue culture) from the animal methods (embryo transplants, adult cell cloning), and remember which produces identical offspring from the best animals versus a copy of one existing adult.
For evaluation questions, weigh the benefits (many desirable organisms, conservation, research) against the concerns (reduced variation, cost, difficulty, ethics). Use precise terms — clone, nucleus, surrogate, tissue culture — throughout.
Quick revision summary
- A clone is a genetically identical copy; cloning is asexual reproduction.
- Plant cloning: cuttings (grow a piece of the parent) and tissue culture (grow many plants from small groups of cells in sterile conditions).
- Embryo transplants: split an early embryo into identical parts and implant each into a surrogate — many identical offspring from the best animals.
- Adult cell cloning: remove an egg's nucleus, insert an adult body cell nucleus, shock it to divide, implant the embryo in a surrogate — a clone of the adult (e.g. Dolly the sheep).
- The clone is identical to the animal that supplied the nucleus, not the egg donor or surrogate.
- Benefits: many desirable organisms, conservation, research; concerns: little genetic variation, cost, difficulty and ethics.