Mad science skills for kids: Crime Scene Investigators: How to Extract DNA in your kitchen

We are living during an exciting scientific revolution that impacts almost every aspect of our lives. At the heart of this revolution is a molecule called Deoxyribonucleic acid or more commonly DNA.  DNA is found in every cell of all living things. You can think of DNA like the blueprint for a life form. Scientists have even learned to take DNA from a plant, animal, or bacteria and put it into a different species. This is called genetic modification. For example, scientists have discovered a piece of DNA called a gene in lightning bugs that causes them to glow. When they put the gene into other types of life they also glow. You can even buy fish that glow due to the insertion of a gene from a lightning bug. Usually, genetic modification is used to benefit society. It is estimated that approximately 70 percent of the food we eat has been in some way genetically modified.

When most people hear DNA, they probably think of the popular television series CSI. This thinking is so widespread that it has created problems in prosecuting criminal cases. Dubbed the “CSI effect,” jurors demand forensic evidence like they see on television that can provide indisputable proof of the identity of a criminal.

DNA was first used forensically in 1985, but the process was expensive and time consuming. Essentially, DNA is cut into fragments with enzymes, the fragments are then separated by size with electricity, and the result is a unique series of DNA fragments called a DNA fingerprint. DNA evidence can identify someone with almost  100 percent certainty because like fingerprints no two people have the same genetic profile. Therefore, a DNA fingerprint can be compared to other samples to determine if the DNA came from the same source. We do not always leave fingerprints and when we do, they do not last long, however we are constantly shedding cells which DNA can be extracted from and the DNA can remain intact for many years.

You can extract DNA from almost anything that is or was alive with common household items. *

DNA extractionMaterials:

• 91% isopropyl (rubbing alcohol) kept in freezer
• Liquid dish detergent
• Non iodized salt or meat tenderizer
• Biological sample for DNA (strawberries or peas are often used, but almost anything biological will work if you have enough cells. You will need about two to three strawberries or about 3 tablespoons)
• Coffee stirrer or similar shaped object to spool DNA
• Zip-top plastic bag.
• Cheese cloth or strainer
• Small container or test tube, if available

Procedure:

1. The first step is to break open the cells of your biological sample, such as strawberries. This can be done by mashing the strawberries in a bag, blending them, or crushing in a bowl with a spoon.
2. Once the sample is broken down,  add about 2 tablespoons of liquid dish detergent and a teaspoon of salt or meat tenderizer and repeat step one. The detergent breaks down the lipid membranes of the cell. Salt or meat tenderizer will help break down proteins in the cell to release the DNA.
3. Strain the sample, preferably with cheesecloth into a container such as a cup or test tube. The purpose is to separate the liquid, which now contains the DNA from the rest of the material. The material in the cheesecloth or strainer can be discarded.
4. Add about 5 tablespoons of cold rubbing alcohol to the strained liquid and stir. The alcohol will cause the DNA to precipitate or turn solid. You will begin to see a white stringy material in the container. This is the DNA.
5. To collect the DNA, twirl a coffee stirrer in the white material to spool the DNA, like you would wrap spaghetti around a fork.
6. To preserve the sample of DNA, transfer the DNA into a sealable container and add enough rubbing alcohol to cover your sample.

*It is possible to extract your own DNA, although it is more difficult because there are fewer cells work with. To extract your own DNA, Gargle with mouthwash for about a minute, and then spit it into a cup. Follow the above procedure, starting from step two.

Once DNA is extracted it has to be processed to create a DNA fingerprint. The process of creating a DNA fingerprint requires materials and tools that are costly and not readily available. However, there are many websites where you can do it virtually. A good website that can be used by kids of any age is http://www.pbs.org/wgbh/nova/teachers/body/create-dna-fingerprint.html.   There is a scenario which directs you to solve a crime through a DNA fingerprint.  You virtually do all of the steps that would be done in a real laboratory to create a DNA fingerprint. When you are finished, you get the chance to compare your DNA fingerprint to those of the suspects. Case Closed.

By Jason Gvazdauskas