Protocol for the Extraction of Human Genomic DNA

Here is a first usable and tested draft of my protocol for human genomic DNA extraction. It isn't meant to produce lab grade products that would be suitable for PCR, but should be pure enough for analysis by means of a basic gel electrophoresis setup (not tested yet), and was created for a high school science demonstration. I've tried to include some of the basic considerations for doing this project on larger or smaller scales (I've tested between 20 mL and 200 mL cell solution scales), and at this time have excluded the use of a centrifuge step (which will be included in a different version once I get my centrifuge and have time to test the rough draft protocol I have prepared for it). Hopefully this is a little clearer than some of the "MacGuyver" protocols out there, and has been explicitly tested on extracting human DNA.

Human Genomic DNA Extraction:

1. Rinse mouth for ~1 minute using a solution of Gatorade, for large sample sizes you can rinse multiple times.

2. Spit solution into a straight walled beaker of suitable size (see further steps to determine size needed).

3. Measure out and add a quantity of detergent in a ratio of 3 mL detergent/20 mL of cell solution.

4. Stir the solution by a method appropriate for the volume of materials used (for single mL volumes in a microcentrifuge tube, invert; for a 1L beaker, stir with a stirring rod).

5. Add an undetermined as of yet "pinch" of meat tenderizer to the solution. (to be quantified in version 2)

6. Stir again until the meat tenderizer is completely in solution and allow ~5 minutes for it to do it's work.

7. Carefully pour the completed solution into a test tube, graduated cylinder, or other container that will allow a low area of surface at the top of the solution in comparison to its volume.

8. Carefully pour 2x the volume of the cell solution of cold (0 degrees C) alcohol (70%> isopropyl alcohol or lab grade ethyl alcohol) into the cylinder, pouring down the side so as not to create an emulsion at the interface between the two separated layer of solutions.

9. Wait for a time while the DNA (and pollutants such as RNA, etc) precipitate at the interface between the alcohol and the cell/detergent solution.

10. For large volume extractions (such as a 200 mL cell solution and 400 mL of alcohol), it can be helpful to stir the alcohol layer such that it agitates the lower layer into a sort of inverse vortex, allowing more of the cell solution to interface with the alcohol over a shorter period of time, while still mostly preserving the division of the layers.

11. Do what you will with the DNA present. Over a period of time (varies depending on volume from 10 minutes-hours) the DNA will settle onto the bottom of the alcohol layer for easier siphoning off to do further studies, or it can be held there for an undefined period of time as something that simply looks cool (will stay intact for at least a day).

The pertinent ratios of chemicals here is the 3 mL detergent/20 mL solution (for consumer grade detergents) which seems to work well for lysing the cells while not creating to much of a mess in the way of bubbles (which make your interface later in the experiment less defined). Also, the ratio of 2x the volume of cell solution in alcohol seems to facilitate visual inspection of the DNA, as well as providing room for error in pipetting off a DNA sample.

Here's a link(Picasa) to a gallery of a few pictures from my smart phone of the result of this extraction being used on a 200 mL cell solution.

I know this isn't by far a perfect protocol, and there are still a lot of unquantified variables and amounts, but that should change over the coming few weeks.