📖 In-Depth Theory
Plant Cloning
Plants can be cloned relatively easily using two main methods:
TAKING CUTTINGS:
A stem or leaf cutting is taken from the parent plant.
The cut end is dipped in rooting hormone and planted in soil.
The cutting develops roots and grows into a new plant — genetically identical to the parent.
Used for: roses, geraniums, herbs, many houseplants.
Advantages: simple, cheap, fast.
TISSUE CULTURE (MICROPROPAGATION):
A tiny piece of plant tissue (explant) is removed — from the growing tip (meristem).
Placed on nutrient agar with plant hormones.
Cells divide and form a callus (undifferentiated mass of cells).
Callus is transferred to medium with different hormones → forms shoots and roots.
Thousands of identical plants produced from a single parent.
Advantages: produce many plants quickly, disease-free plants, preserve rare species.
Disadvantages: expensive, requires specialist equipment and sterile conditions.
Animal Cloning — Embryo Transplants
Animal cloning is more complex than plant cloning.
EMBRYO TRANSPLANTS:
1. A female is given fertility drugs → produces multiple eggs.
2. Eggs are fertilised IN VITRO (outside the body) using selected sperm.
3. The developing embryo is split into multiple pieces before cells differentiate.
4. Each piece develops into a genetically identical embryo.
5. Embryos are transplanted into SURROGATE MOTHERS who carry them to birth.
Used in: cattle and sheep farming to produce multiple offspring from genetically superior parents.
NUCLEAR TRANSFER (SOMATIC CELL NUCLEAR TRANSFER):
The technique used to produce Dolly the sheep (1996).
1. Nucleus removed from an unfertilised egg (enucleated egg).
2. Nucleus from an adult body cell (somatic cell) inserted into the enucleated egg.
3. Electric shock stimulates cell division.
4. Embryo develops and is implanted into a surrogate.
5. Offspring is genetically identical to the adult whose nucleus was used.
Dolly was the first mammal cloned from an adult cell — a major scientific breakthrough.
Advantages and Disadvantages of Cloning
ADVANTAGES:
Preserve ENDANGERED SPECIES — clone animals at risk of extinction.
Produce genetically SUPERIOR animals — all offspring inherit the best traits.
Medical research — produce animals with human diseases for drug testing.
Potential to produce organs for transplant (therapeutic cloning).
Preserve rare PLANT VARIETIES and produce disease-resistant crops.
DISADVANTAGES:
REDUCES GENETIC DIVERSITY — large population of identical organisms vulnerable to same disease.
ETHICAL CONCERNS about cloning humans (reproductive cloning).
CLONED ANIMALS often have health problems — Dolly developed arthritis and lung disease early.
Expensive and technically difficult (animal cloning especially).
Low SUCCESS RATE for nuclear transfer — many attempts needed to produce one viable clone.
ETHICAL DEBATE:
Therapeutic cloning (for medical treatment) vs reproductive cloning (creating cloned organisms) — different ethical considerations.
Scientific community broadly supports therapeutic, opposes reproductive human cloning.
⚠️ Common Mistake
Clones are genetically identical but NOT necessarily physically identical — environment (temperature, nutrition, upbringing) affects how genes are expressed. Dolly was genetically identical to her donor but didn't look exactly the same. Genotype ≠ phenotype.