5.17B-5.20B - Cloning - micropropagation and cloned animals

Core cloning terms

A clone is a genetically identical copy. Clones can be cells, tissues or whole organisms. The important point for this cluster is that the copied organisms have the same genetic information as the original source, unless a mutation occurs.

Micropropagation is plant cloning by tissue culture. It starts with an explant, which is a small piece of plant tissue taken from a selected parent plant.

The explant is grown in vitro. This means it is grown outside a living organism, in artificial laboratory conditions such as on sterile agar in a dish or tube. Do not confuse in vitro with "inside the plant" or "controlling variables"; it literally means grown outside the organism.

The animal-cloning part uses different vocabulary. A mature body cell has a diploid nucleus, meaning it contains the full set of chromosomes. An enucleated egg cell is an egg cell whose nucleus has been removed.

Micropropagation method

Micropropagation uses tissue culture to produce plant clones. It works because small pieces of plant tissue can divide and develop into whole plants when they are given the right sterile conditions, nutrients and plant growth substances.

The usual Pearson-style sequence is:

1. Choose a parent plant with desirable characteristics, such as high yield, disease resistance or attractive flowers.
2. Cut very small pieces of tissue, called explants, from the plant using sterile forceps or a scalpel.
3. Sterilise the explants, for example with bleach, hypochlorite or ethanol, then handle them using aseptic technique.
4. Place the explants onto sterile agar or another growth medium.
5. The medium contains nutrients, such as glucose, minerals or amino acids, and plant growth substances or hormones.
6. Incubate the explants in controlled conditions so cells divide by mitosis and form a callus, shoots or small plantlets.
7. Transfer the plantlets to a rooting medium if needed, then grow them in a glasshouse before planting outside.

[DIAGRAM: asset_name: Cloning: micropropagation and cloned animals - diagram 01; asset_slug: b68_cloning_micropropagation_and_cloned_animals__diagram_01; recommended_method: deterministic_drawing; description: Monochrome flow diagram showing micropropagation from a selected parent plant with desirable characteristics to small explants, sterilisation, sterile agar with nutrients and plant growth substances, in vitro growth into callus/shoots/rooted plantlets, glasshouse hardening and many genetically identical plants.]

Sterile technique matters because bacteria and fungi grow well on nutrient agar too. If microorganisms contaminate the culture, they can outcompete or kill the plant tissue. In exam answers, "put the explant in soil" is not enough for micropropagation; the key setting is sterile in vitro culture.

Commercial plant clones

Micropropagation is useful commercially because it can make many copies from one valuable parent plant. If the parent has a desirable characteristic, the clones should have the same characteristic because they are produced by mitosis and are genetically identical.

The phrase "commercial quantities" means large numbers suitable for nurseries, farms or horticulture, not just one or two classroom samples. A strong answer often says both parts: many plants are produced and the plants are genetically identical with the desired characteristic.

Micropropagation is asexual reproduction, so it does not use pollination, gametes or fertilisation. Pollination and sexual reproduction can create genetic variation, which is useful in some situations but not when growers need many identical copies of one successful plant.