Cloning (AQA GCSE Biology): Revision Notes
Cloning
What is cloning?
Cloning means making organisms that have exactly the same genes. Plants and animals can be cloned to create many genetically identical individuals. This is very useful in farming and conservation, allowing scientists and farmers to reproduce organisms with desirable characteristics.
The term "clone" comes from the Greek word "klon," meaning twig or branch, reflecting how plants naturally reproduce identical copies through vegetative propagation.
Cloning plants
There are two main ways to clone plants, each with its own advantages depending on the scale and purpose of cloning needed.
Tissue culture method
This scientific method involves growing new plants from tiny pieces of tissue. Here's how it works:
- Take a sample - Cut a small piece of tissue from the parent plant
- Place on agar jelly - Put the tissue on special jelly that contains plant hormones and nutrients
- Watch them grow - The tissue samples develop into tiny plants
- Transfer to soil - Move the new plants to trays of compost to continue growing
The tissue culture method requires sterile conditions to prevent contamination by bacteria and fungi, which could kill the developing plant tissues.
This method is important because it helps us:
- Save rare species of plants from extinction
- Produce lots of plants quickly for nurseries
Taking cuttings
Gardeners often use this simpler method. They take cuttings from a parent plant and grow them into many new plants that are identical to the original.
Cloning animals
Animal cloning involves more complex procedures than plant cloning, requiring sophisticated laboratory techniques and equipment.
Embryo transplant
This method works by using embryos (very early stage babies) before their cells become specialised:
- Fertilise eggs - Sperm fertilise eggs to create embryos
- Separate cells - Take apart the embryo cells before they develop specific jobs
- Grow separately - Each cell grows into a complete new embryo
- Transplant - Put these genetically identical embryos into different host mothers
The timing is crucial in embryo transplant - the cells must be separated before they become specialised (differentiated) into specific cell types, which happens very early in development.
The babies that are born are clones of the original embryo.
Adult cell cloning
This more complex method creates clones from adult body cells:
- Remove nucleus - Take the nucleus (containing genes) from an adult body cell
- Prepare egg cell - Remove the nucleus from an unfertilised egg cell, leaving it empty
- Insert nucleus - Put the adult cell nucleus into the empty egg cell
- Electric shock - Give the cell an electric shock to start it dividing
- Cell division - The cell divides to form an embryo
- Implant - Put the embryo into a female's womb to develop until birth
The offspring will be genetically identical to the adult that donated the body cell.
Worked Example: Dolly the Sheep
Dolly was the first mammal cloned from an adult cell in 1996:
- Scientists took a nucleus from an adult sheep's mammary gland cell
- They inserted it into an empty egg cell from another sheep
- After an electric shock, the cell began dividing
- The resulting embryo was implanted into a surrogate mother
- Dolly was born as a genetic copy of the mammary gland cell donor
Why is cloning useful?
- Agriculture - Farmers can produce many animals with desired traits like high milk production or disease resistance
- Conservation - We can save endangered species by preserving their genetic material
- Medicine - Cloning can help produce organs for transplants and test new treatments
- Research - Scientists can study diseases better using identical animals as test subjects
While cloning offers many benefits, it also raises ethical questions about genetic diversity, animal welfare, and the naturalness of reproduction that continue to be debated by scientists, ethicists, and society.
Key Points to Remember:
- Cloning creates organisms with exactly the same genes
- Plants can be cloned using tissue culture or cuttings
- Animals can be cloned using embryo transplant or adult cell cloning
- Embryo transplant uses cells before they specialise
- Adult cell cloning transfers a nucleus from a body cell to an empty egg cell
- Cloning is useful for farming, conservation and medical research