Cloning is definitely one of the more popular themes in science fiction movies but with the recent progress in research, it has already turned into reality. Cloning is not a completely human-made process; there are many examples of it in nature including binary fission in bacteria or propagating plants with plant cuttings. However, we have managed to develop techniques to clone organisms which don’t naturally reproduce in this way. In this article, we will explore different types of cloning, and see where it might take us next.
There are three types of cloning: gene, therapeutic and reproductive cloning. They require different mechanisms and are done for different purposes. We will describe them one by one and cover the most important techniques involved in them.
Gene cloning involves copying specific genes or segments of DNA, e.g. to produce human insulin or introduce specific characteristics to species. This type of genetic modification often uses bacteria and other microscopic organisms as vectors. Let’s take a look at the steps involved in this type of cloning:
Firstly, a gene which we want to clone is extracted from eukaryote and converted into complementary DNA (cDNA) using an enzyme called reverse transcriptase. This is done to remove introns from eukaryotic DNA because bacteria don’t have them in their DNA so they couldn’t process them.
plasmid (a small snippet of bacterial DNA) is cut using restriction endonuclease to produce two sticky ends. That’s where our cDNA will join.
DNA ligase ‘seals’ the sticky ends with cDNA. That’s how we get our recombinant plasmid.
The recombinant plasmid is introduced to bacteria which then grow and multiply producing more and more plasmids with our desired genes
Reproductive cloning produces an identical organism to an organism of a cell donor. This type of genetic modification is probably the most famous thanks to Dolly the sheep. Here is how the scientists cloned this organism:
to successfully carry out this genetic modification, scientists needed 3 sheep: a cytoplasmic donor, an egg donor and a surrogate
the egg from the cytoplasm donor was enucleated (only its nucleus was extracted)
the nucleus from the egg donor’s egg was removed and the nucleus from the cytoplasmic donor was fused with the egg donor’s cell
electric spark was passed through the egg to initiate division
the blastocyst (the egg after it divided for certain amount of time) was transferred to the surrogate sheep
Therapeutic cloning occurs in a very similar way as reproductive cloning; however, it is used for different purposes. In terms of procedure, the only difference between therapeutic and reproductive cloning is that the modified egg is not transferred to any surrogate organism. Instead, it is grown in a lob and induced to differentiate into different cell types (neurons, lymphocytes etc). Those stem cells can be then used to treat various diseases, e.g. the Stargardt’s disease.
WHAT ARE SOME ISSUES RELATED TO CLONING ORGANISMS?
First of all, reproductive cloning is quite inefficient because only a small percentage of embryos actually survive. Moreover, we can’t predict mutations which might occur in those organisms. We also need to think about various ethical dilemmas related to cloning such as killing artificially produced embryos for stem cells or generally, using genetic modification to treat human diseases which is associated with some risks.
HOW COULD CLONING CHANGE MEDICINE?
Research of genetic modification has such a huge potential that it is hard to summarize to what extent it could revolutionize the medical field. Thanks to cloning, we could treat many currently untreatable diseases which involve tissue degeneration such as Alzheimer’s or maybe even heart attacks. If we put the ethical considerations aside for a moment, embryonic stem cells created via cloning could be modified to contain certain genetic diseases so that scientists can use them to test new treatments. However, as you can imagine, there are many ethical issues related to such research and we might not be able to carry out those investigations for a long time.
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Lakna. (2019, December 23). What is the Difference Between Therapeutic and Reproductive Cloning. Pediaa.com. https://pediaa.com/what-is-the-difference-between-therapeutic-and-reproductive-cloning/#Reproductive%20Cloning
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