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Asked by andreaslevin to Enda, Jean, Kate, Kev, Tim on 18 Nov 2012.
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Tim Downing answered on 18 Nov 2012:
Hi Andreas,
Please see the answer I gave you on cloned bananas. There I mentioned that most life reproduces by cloning (ie asexually) – not just bacteria but most plants and some species of lizards too. Note also that even for clone’s DNA here, it will never be the exact same as the parent’s: mutations can occur, and also DNA in species like lizards and plants will re-shuffle (called recombination). Lizards and plants generally have 2 copies of each chromosome: each chromosome has its own set of mutations. Recombination mixes these sets of mutations up, and can cause new effects with the same set of genes. So even if clones are nearly genetically identical, they can have different outcomes.
Our DNA is stored in a cell compartment called a nucleus, where it is wrapped carefully around proteins to prevent damage. In principle it is possible to transfer DNA from one nucleus to another, see this video
So we could transfer DNA from one of your cells into an egg cell whose nucleus has been removed. With an electric shock, this egg cell with your DNA would then divide. But in practise this is tricky to do properly since even the tiniest mistake would mean the cell would eventually stop dividing properly. This approach was first use to make amphibian clones in 1928 and more famously in 1996 in a sheep (Dolly).
The main useful aspect of cloning is the potential to replace faulty cells, tissues or organs. Though very challenging, it is possible to grow tissue in the lab and transfer it to patients. So this approach could for example be used to treat someone with liver disease.
Tim
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Jean Bourke answered on 19 Nov 2012:
Humans could theoretically be cloned as can any living thing. The how is the hard part and that’s without getting into the morals of it.
The problem with cloning is that the transferred DNA (see Tim’s answer) often does not behave properly. The more complicated the animal, the more things there are to go wrong.
This is because of something we call differentiation. When we start off as embryos our cells are undifferentiated, they are all exactly the same. Over time thought they take on special roles and are now differentiated. They are each designed to do something specific, you can’t make a skin cell suddenly act like a nerve cell coz it has differentiated already and doesn’t know how to change. Stem cells are a big deal because they are undifferentiated and have the potential to become any kind of cell! That is why they have a lot of potential in medicine.
If we take the DNA from one cell and put it into an egg cell (that has had its DNA removed) there is no guarantee that the DNA will act the way its supposed to and allow the egg to grow properly.
This cause a lot of difficulties when cloning was first being investigated. You can get a cell to undiffentiate a bit by giving it certain signals. But it will only do so a little and it is an imperfect process.
Cloning a human would be very hard but, as Tim said, cloning a bit of one might be achieved much more easily (and without any worrying moral implications).
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