It’s easy to extract DNA from bananas, strawberries, or other polyploid plants. Human cells are diploid, which means each cell nucleus contains two copies of each chromosome (one from each parent). Polyploid cells contain multiple copies of chromosomes, so there is more DNA to collect.
Here is a simple DNA extraction method you can do at home using common, safe materials.
DNA extraction is not complicated. You only need a few basic ingredients.
- Banana (or strawberries or human cheek cells)
- Distilled water
- Dishwashing liquid
- Rubbing alcohol
- Plastic bag OR blender or smoothie maker
- Coffee filter or paper towel
- Toothpick, wooden skewer, or glass rod
- Distilled water is better than tap water because it has a neutral pH and is free of impurities. But, if you don’t have distilled water, tap water usually works fine.
- Ideally, use a translucent dishwashing liquid (not one that looks cloudy or pearlescent). Shampoo containing sodium lauryl sulfate works too. Just make sure it’s not a conditioning shampoo.
- Use regular table salt (NaCl).
- Either isopropyl alcohol or ethanol work for this project. Choose rubbing alcohol (isopropyl alcohol) with a high alcohol content. For the best results, choose 91%, 95%, or 99% (not 60% to 75%). Alternatively, use denatured alcohol (ethanol). Store the alcohol in the freezer to chill it before use.
How to Extract DNA From a Banana
You can perform the project in a plastic bag or you can use a test tube or small glass. There is nothing dangerous in this project (but don’t drink it), so you can use kitchen glassware safely and then wash it before using it with food. You’ll get a better extraction using a blender or smoothie maker rather than a plastic bag, but a banana has enough DNA that the plastic bag method works fine.
- Either blend 1 banana and 1/2 cup water or else place the ingredients in a plastic bag and squish them well.
- In a small cup, mix 1 teaspoon of dishwashing liquid, 1/4 teaspoon salt, and 2 tablespoons water. Stir gently to dissolve the salt, but don’t swish around the soap and form a foam.
- Add 2 tablespoons of banana mixture to the detergent mixture. If you’re using a plastic bag, add the detergent mixture to the bag containing the mashed banana.
- Thoroughly mix the ingredients.
- Filter the liquid through a coffee filter or paper towel. A good method is securing the filter over a glass using a rubber band. Or, place the filter inside a funnel and set the funnel over a glass. Because the mixture is thick, it takes time for the liquid to make its way through the filter. Resist the urge to squeeze the filter paper and speed up the process.
- After about 10 minutes, collect the liquid (the filtrate). You can discard the banana and filter paper.
- Drip about 15 milliliters of cold alcohol onto the liquid. Do not stir it. Ideally, you should see a layer of alcohol on top of the banana liquid. Let the alcohol and filtrate sit undisturbed for 4-5 minutes. The DNA precipitates as cloudy or white cottony material at the interface between the alcohol and the banana layers.
- Dip a toothpick, wooden skewer, or thin glass rod into the liquid and slowly rotate it to spool out the DNA. Examine the DNA, using a magnifying glass if available. If you have a microscope, place the blob of DNA onto a slide. Gently tease apart the DNA strands using a toothpick so you can see them better.
How Extracting DNA From a Banana Works
- Mashing the banana increases the surface area of the plant cells and makes extracting the DNA easier. Add water helps separate the cells from each other. The better you blend the banana, the more efficient the extraction.
- Detergents and other surfactants from dishwashing liquid break down the lipid bilayer of the cell wall (in plants), cell membrane, and nuclear membrane.
- In a laboratory setting, enzymes called proteases break down proteins so they can be separated from DNA.
- A lab might add enzymes called ribonucleases to break down RNA, too.
- Salt or sodium chloride removes proteins bound to the DNA and helps the DNA clump together.
- DNA precipitates out of solution in ice-cold alcohol. If the alcohol is too warm, some of the DNA remains dissolved.
- In a lab, the next step is centrifugation. The centrifuge collects the solid DNA as a pellet, so more of it is recovered from the mixture.
DNA Extraction History
DNA extraction predates the discovery of DNA as a molecule. In 1869, Swiss biologist and physician Friedrich Miescher extracted DNA from white blood cell nuclei. He theorized the material he collected play a role in heredity. Since Miescher’s time, scientists have refined extraction methods. In place of alcohol, phenol and chloroform better separate proteins from DNA. Restriction enzymes and polymerase chain reaction (PCR) help researchers amplify DNA, meaning it’s possible to make many copies of DNA from a tiny sample.
- Dahm, R. (January 2008). “Discovering DNA: Friedrich Miescher and the early years of nucleic acid research”. Human Genetics. 122(6): 565–81. doi:10.1007/s00439-007-0433-0
- Li, Richard (2015). Forensic Biology (2nd ed.). Boca Raton: CRC Press. ISBN 9781439889701.
- Marmur, J. (1961). “A procedure for the isolation of deoxyribonucleic acid from micro-organisms”. Journal of Molecular Biology. 3 (2): 208–IN1. doi:10.1016/S0022-2836(61)80047-8
- Pääbo, S. (March 1989). “Ancient DNA: extraction, characterization, molecular cloning, and enzymatic amplification”. Proceedings of the National Academy of Sciences of the United States of America. 86 (6): 1939–43. doi:10.1073/pnas.86.6.1939
- Sambrook, Michael R.; Green, Joseph (2012). Molecular Cloning. (4th ed.). Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press. ISBN 1936113422.