Production of Artificial Clones in Animals (OCR A Level Biology)

Embryo twinning

• The process of embryo twinning produces offspring that are clones of each other but not of their parents
• It has been a routine procedure carried out to boost yields of livestock and promote desirable characteristics since the 1980s
• The key step is the deliberate division of the embryo into two half embryos
• These are then inserted into a surrogate mother for gestation and birth
• The surrogate gives birth to identical twins
• In some cases, embryos are split into single identical cells, each of which can be implanted into a separate surrogate mother animal
• Although embryo twinning guarantees desirable characteristics in the offspring, it is not possible to predict how many offspring will be produced

Embryo twinning of cattle by splitting the embryo

Reproductive cloning

• This is the method made famous by Dolly the sheep, cloned in Edinburgh, UK in 1996
• Its name is Somatic Cell Nuclear Transfer (SCNT)
• Dolly made headlines as being the first livestock animal to be created from a clone
• Three separate animals are required:
  • The animal to be cloned by donating a cell
  • The female to donate an egg cell
  • The surrogate mother

• How the procedure is carried out:
  • The animal to be cloned donates a somatic (body) cell eg. from an udder
  • The egg cell is extracted from the egg donor and enucleated (its nucleus is removed by suction and discarded)
  • The nucleus from the udder cell is injected into the enucleated egg cell
  • The hybrid zygote cell is now treated to encourage it to divide by mitosis
  • The embryo is implanted into the surrogate mother for gestation and birth

Reproductive cloning of animals.

Therapeutic cloning

• This is a technique designed to use cloned cells to replace dead or damaged cells that cause a loss of function in an individual
• Embryos are cloned as in reproductive cloning, but the embryos are removed and subdivided
• Each individual embryo cell is a totipotent stem cell that can be cultured and artificially differentiated into any type of specialised cell
• In theory, any specialised cell can be derived by this method
  • Crucially, specialised cells with the same genome as the sufferer can be cloned and replaced

• An example is replacing specialised brain tissue in sufferers of Parkinson's Disease
• At present, there is a lot of potential for therapeutic cloning but little clinical progress has been made