OCR A Level Biology

Revision Notes

6.4.6 Production of Artificial Clones in Animals

Production of Artificial Clones in Animals

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 1, downloadable AS Level & A Level Biology revision notes Embryo twinning 2, downloadable AS Level & A Level Biology revision notes
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

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

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