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Gene Cloning

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Gene cloning is a process in which we insert a section of DNA into a cell and then let the cell undergo mitosis, creating copies of that genetic information. Gene cloning is different from organism cloning, which uses an organism's DNA to produce a genetically identical organism, because it only produces cells, not an entire organism. To clone genes, scientists "cut" out a specific gene using a restriction enzyme, "glue" it into a vector DNA using the enzyme ligase, then insert the vector DNA into bacteria which reproduces, thus cloning this new DNA along with its own.

When people hear the term genetic cloning they immediately focusing on what how good it's presented which is things like in Star Wars where all of a sudden you have mass of armies of clones or some TV show or late night scifi movie when you kill the villain but the next month his clone is back. In reality genetic cloning is a lot less complicated. The basic idea is what's called genetic cloning is you're making copies of DNA. Now you can talk about it at the individual gene level and that's what scientists often do or you can talk about cloning an entire organism.

Now let me go through the basic process of how you do gene cloning and then I'll talk about cloning an entire organism, so the idea of gene cloning is that you take a section of DNA that you're inrested in like a gene and you insert it into some other cell a host who grows up and every time that host cell copies it's own DNA he winds up copying the DNA that you'd added to it your desired clone so you begin by cutting the desired DNA out from whatever source it has you do this using a special enzyme called a restriction enzyme then you glue that DNA into some other DNA called a vector DNA and the process of gluing DNA is called ligating using an enzyme called ligase. You then insert our newly combined DNA with the vector DNA into your host cell then once that host cell has the vector DNA in it it starts to grow now you can never quite be sure which cell in your test tube got that DNA versus which ones did not and that's why you have to do what's called select for expression look to see is it expressing or showing its new traits.

Organism cloning is where you take the nucleus from one organism say me and you take this nucleus and you put it into an egg cell from some other donor organism and by replacing the original eggs nucleus with mine, we can now implant this newly created egg cell into a some surrogate mother who gives birth to little baby me. You've actually seen this process done before only without a lot of this manipulations its how we get identical twins because you started off with one cell it started dividing made a ball cells got separated in two identical balls of cells and those grew into genetic copies so identical twins are examples of natural clones.

But let's take a look at how we do this genetic cloning a little bit more in detail so in this diagram here we can see our desired DNA in green the actual gene that we're interested in is in the darkest green way over on the right. This blue circle with some other bits on it is our vector DNA a circle of DNA like this is called a plasmid. Now we cut our original DNA, the green, with a special enzyme called a restriction enzyme that cuts its specific spots on the sequences of DNA we also cut our vector DNA with the exact same of restriction enzymes. We can then mix our combos of DNA and add our ligase enzyme and we get a newly recombined or recombinant plasmid right here. Then we insert that down into a bacterial cell now you can see in red is the bacterial cell's own chromosome but now it has this additional DNA now all we have to do is feed this bacteria and does what bacteria loves to do as well as most other creatures and that's having a little baby bacteria so each baby bacteria has the copy of the original cells chromosome as well as its own copy of our recombinant plasmid. Now in our test tube we'd have other cells that didn't get our vector and so they too will be copying so we don't know which ones have the newly recombinant DNA in them and which ones don't and that's why we'd screw them onto a Petri dish like this and allow them to grow and in this little diagram you can spot the ones that have the plasmid because they're the ones that are growing this bright red let's supposed our desired DNA actually encoded for a red fluorescent protein right? That's gene cloning.

Organismal cloning perhaps the most famous example of this is Dolly the sheep and what they did with to make Dolly the sheep is they got some cells from an adult sheep over here all the way on the right who's donating a nucleus and then they got a egg cell from a different breed of sheep and they took the nucleus out of that egg shell then they combined the a nucleated cell with the nucleus from a mammary cell, they allowed those newly made zygotes essentially to start to grow and got to a point in which they're called a blastocyst which is this big massive cells and they implanted those into surrogate mothers and when those surrogate mothers gave birth they gave birth to a sheep called Dolly who looks just like the original nuclei donor and looks nothing like the surrogate mothers and that's an example of organismal cloning.

Now you may be thinking wow this is awesome I'd love to have a whole bunch of little mini me's you've got to be careful this process is still kind of experimental for example Dolly is the one survivor out of roughly 270 odd failures and a lot of people have some ethical dilemmas about having a 270 human failures. Now obviously if you paid attention to the news you've heard about improvement synthesis and a lot of farmers actually using this to make clones of some of their best animals but still the process, if you make a mistake with the cow you have hamburger if you make a mistake with the human you've got a law suit and that's the problem.