Easy Experiment for Extracting DNA at Home

Mendel’s Peas: A DNA Experiment to do at Home

Gregor Mendel was a nineteenth century monk who demonstrated the basic principles of genetic inheritance via his experiments with pea plants. The significance of Mendel’s work was not recognized until the twentieth century, when several scientists reproduced Mendel’s original experiments. He is now considered to be the founder of modern genetics.

Punnett Square depicting Mendelian inheritance in pea plants. Image by Lady of Hats.

The following is a simple experiment to extract, or precipitate, DNA, which is the carrier of genetic information. DNA is tightly coiled inside the nucleus of a cell, and is protected by proteins and the cellular membrane. Using common household reagents, the following steps will remove those barriers and make DNA visible to the naked eye.

Step 1: Make a Pea Solution

Combine 250 ml (~1 cup) of peas with 1.5 ml (~1/4 teaspoon) common table salt and 500ml (~2 cups) of cold water in a blender, or by using a mortar and pestle. It is essential that the water be cold (ice water is preferable) as the low temperature slows down cellular reactions and will increase the amount of DNA yielded at the end of the experiment.

Step 2: Add Detergent

Strain the pea mixture to remove all solids from the solution, and then add 60 ml (~4 tablespoons) of a liquid laundry detergent. The purpose of the detergent is to release the DNA from the boundaries of the cell membrane and nucleus. Gently swirl the mixture, or carefully stir, and then allow the solution to sit undisturbed for 10 minutes. It is important to refrain from jarring or stirring the solution vigorously, as such actions will break up the fragile DNA.

Step 3: Add Proteases

In normal bodily processes, proteases are enzymes that digest proteins. At this point in the experiment, the DNA is no longer contained within the nucleus, but it is still bound to proteins, which can be purified by adding proteases. For this step, add 1 to 2 drops of contact lens solution, which contains proteases to break down protein build-up on contacts. You can also use a pinch of meat tenderizer to break down the proteins. As in step 2, stir the solution very gently.

Step 4: Add Rubbing Alcohol

Tilt the container holding the solution to about a 45 degree angle, and slowly add chilled rubbing alcohol (isopropyl or ethyl alcohol) to the solution. The rubbing alcohol should be kept cold in an ice bath through the first few steps, as the colder temperature will help the DNA to precipitate from the solution.

White clumps of DNA in solution. Photo by Naturkunste Museum, Berlin

Step 5: Collect the DNA

The alcohol will float on top of the water, and the DNA will begin to precipitate in white, tangled clumps at the layer where the pea solution and alcohol meet. Use a wooden stirring stick, straw, or glass rod to draw the DNA out of the solution. If you don’t see any white clumps or very little, leave the solution to sit for up to an hour. It may take some time for the DNA to precipitate, depending on such variables as temperature, volume of DNA, and reaction speed.

Notes

Be careful when using rubbing alcohol, and wash any spills off the skin immediately. If possible, wear eye protection while performing the experiment. In a lab setting, once the mass of the precipitated DNA is obtained, researchers may stain it, to visualize the DNA in greater detail.