Actually this post will describe how to extract DNA from a banana, a tomato and from yourself. The method is similar for all three.
Extracting DNA samples
I gave the children the choice of extracting DNA from tomatoes, bananas or from themselves. It is very easy to do requiring nothing more than water, salt, surgical spirit, clear washing up liquid, coffee filters, food dye and a tissue sample (salt water washed round in the mouth, smashed banana mixed with salt water, smashed tomato mixed with salt water).
Set Up your Work Stations
Set up three different work stations with all the need equipment to extract the DNA, including an instruction sheet:
Create a Tissue Sample
This will be a sample of salt water which has millions of cells suspended in it. To do this, mix a teaspoon of salt with half a cup of bottled water:
Smash the banana or tomato flesh in a zip lock bag. Add salt water solution and mix carefully. For your own tissue sample use the salt water as a mouth water and gargle for one minute suspending cheek cells in the water and carefully spit into a clear beaker:
Add a half a teaspoon of dish soap to the zip lock bags (or if doing your own DNA add a couple of drops to the gargled suspension in the beaker). Mix gently trying not to create too much foam. The soap acts to break down the cell membrane releasing the DNA into the suspension:
Pour the contents of the zip lock bags through a coffee filter sitting over a funnel over a clear glass beaker. Leave awhile whilst it collects a liquid suspension of water, soap and tomato or banana DNA:
Extract the DNA
In a separate cup mix 100mls of surgical spirit and a few drops of food colouring:
Gently pour the alcohol down the side of the beaker containing the suspended tissue sample (tip beaker):
It should form a layer on top of the sample. Leave for a few minutes:
At this point you should notice a few strands or clumps of a white substance. These are the DNA strands clumping together. Using a stirrer you may be able to pick up some of the strands:
You have extracted your DNA!