Understanding:
• Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells
At a very early stage, embryonic cells retain pluripotency (meaning they can divide and become any type of tissue)
- These cells will differentiate to form all the different tissues comprising the organism
If these embryonic cells are separated artificially in the laboratory, each group of cells will form cloned organisms
- This separation of embryonic cells can also occur naturally to give rise to identical (monozygotic) twins
The separation of embryonic cells has to happen early in the developmental cycle, ideally around the 8 cell stage (morula)
- The separated groups of cells are then implanted into the uterus of a surrogate to develop into genetically identical clones
This method of cloning is limited by the fact that the embryo used is still formed randomly via sexual reproduction and so the specific genetic features of the resulting clones have yet to be determined
Cloning via Embryonic Division
Understanding:
• Methods have been developed for cloning adult organisms using differentiated cells
A second and more reliable method of artificial cloning involves somatic cell nuclear transfer (SCNT)
- This involves replacing the haploid nucleus of an unfertilised egg with a diploid nucleus from an adult donor
- The advantage of this technique is that it is known what traits the clones will develop (they are genetically identical to the donor)
This method of using differentiated cells to generate cloned embryos can be used for two main purposes:
- Reproductive cloning: If the embryo is implanted into the uterus of a surrogate, a new cloned organism will develop
- Therapeutic cloning: Embryonic cells can be induced to differentiate to create specific tissues or organs for transplantation
Comparison of Reproductive and Therapeutic Cloning
