• Tissue culture is a process in which very small pieces of plants (‘tissue’) are grown (‘cultured’) using nutrient media
• Because they are initially grown in petri dishes on nutrient agar we say they are grown ‘in vitro’ – outside a living organism
• How to propagate plants in vitro:
  • Cells are scraped from the parent plant (these cells are known as explants)
  • The cells are transferred to a sterile petri dish containing nutrient agar
  • Hormones (eg. auxins) are added to encourage plants to grow into small masses of tissue (callus tissue)
  • Tissue continues to grow and forms plantlets that can be transferred to individual potting trays and develop into plants

Tissue culture: using small groups of cells from part of a plant to grow identical new plants

• Clones are genetically identical individuals
• The cloning of plants has many important commercial uses
• It allows a variety of a plant with desirable characteristics to be produced:
  • cheaply
  • with a greater yield (a large number of plants can be produced)
  • quickly
  • at any time of the year
• It can also ensure diseases prevalent in other areas of the world are not imported and spread by ensuring native varieties of plants are produced in large enough quantities to supply demand in one country without importing plants from abroad
• Tissue culture can also be an important process in preserving rare plant species

• An older and more simple method to clone plants (mainly used by gardeners) is by taking cuttings
• Gardeners take cuttings from good parent plants (eg. those that are healthiest and best-looking) – a section of the parent plant with a new bud is cut off
• These cuttings are then planted and grow into genetically identical versions of the original plant
• Plants cloned by taking cuttings can be produced cheaply and quickly

• It is possible to clone animals using embryo transplants
• For example, if a farmer wants the best cattle, they must first create an offspring from the best bull and best cow, and then clone this offspring to create many genetically identical copies (clones)
• This process is known as embryo cloning and is achieved in the following way:
  • Egg cells from the best cow are artificially fertilised using sperm cells taken from the best bull
  • This forms an embryo
  • The developing animal embryo is then split apart many times before the cells of the embryo become specialised
  • This forms many separate embryos that are genetically identical
  • These cloned embryos are then transplanted into host mothers
  • The calves born from these host mothers are all genetically identical

Embryo cloning

• Adult cell cloning is achieved in the following way:
  • The nucleus is removed from an unfertilised egg cell
  • The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell
  • A very small electric shock stimulates the egg cell to divide (by mitosis) to form an embryo
  • These embryo cells contain the same genetic information as the adult skin cell
  • When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female (known as the surrogate mother) to continue its development until birth
• This process was used to create the first clone (exact genetic copy) of a mammal in 1996
• Scientists in Scotland successfully cloned an adult female sheep
• The clone was called Dolly

Adult cell cloning: the cloning technique used to produce the first cloned mammal, Dolly the sheep

Benefits & risks of cloning table