I am excited to report that the experiment for this week are inspired by a new book, You Can't Wear These Genes by my friend Shirley Duke, who blogs at SimplyScience. Be sure to look for my interview with Shirley and more about the book over at Wrapped In Foil. Shirley will be celebrating her 100th blog post this week at SimplyScience, so you might want to stop over and say hello.
About the book:
You Can't Wear These Genes is an easy-to-understand overview of genetics for children in grades 4-7. Reading this book is a perfect way to introduce a lesson on genes and DNA.
Shirley starts out with an idea a child can relate to, how we inherit traits from our parents. Further inside are explanations of common terms, like chromosomes, alleles, and what a genome is. The crisp clear, illustrations of the structure of DNA, for example, complement the text. Not only does Shirley review the background of what we know so far in the field of genetics, but she also gives us a glimpse of the future by looking at the Human Genome Project, genetic engineering and cloning.
I know I will be using this book when I present the following activity to a group of children next month.
Activity: DNA Extraction From Strawberries and/or Bananas
Believe it or not, these days you can extract DNA from common fruits and vegetables right in your own home.
- strawberries, bananas or both (these fruit contain extra copies of DNA making extraction easier)
- plastic bags that seal (or something to mash the fruit in)
- water, preferably distilled
- a device to measure liquids in ml (optional for a single test, see 1 below)
- dish detergent
- table salt and measuring spoon
- a container to mix the extraction buffer in
- isopropyl alcohol and a way to keep it cold. Most recipes call for 90%, but 70% is acceptable.
- glass container, like a beaker
- funnel (optional)
- filter material such as cheesecloth, coffee filter, paper towel or any old piece of cloth
- test tube or spice jar, and some type of holder to keep it upright
- A medicine dropper (optional)
- wooden stick that will fit in the test tube, such as a craft stick or wooden skewer
Before you start, put the isopropyl alcohol in the fridge or on ice so that it is cold when you need to use it. Note: you can use ethanol, but isopropyl (rubbing) alcohol is cheaper and easier to obtain.
1. If you are working with a group you will need to make the extraction buffer, which is the solution that helps break down the strawberry cells and release the DNA. The basic ingredients are water, dish detergent (or shampoo) and table salt. One common formula is 300 ml water, 25 ml dish detergent, and 1 Tablespoon table salt. Note: Stir this mixture gently. Excessive bubbles will interfere with the extraction process later on.
If you are doing a single test on one strawberry or one piece of banana, there's no need to make up a big container of buffer. Try 2 tsp water, 1 tsp soap, and 1 pinch salt for each berry.
2. Place a single strawberry or 1/2 a banana in the plastic bag, seal and mash it up. You can do one kind of fruit, or do both separately and then compare your results. The plastic bags works well if you are doing this with a group of children because each child can mash his or her own. You can simply mash the fruit in a bowl, too. This should only take a minute or two. If the banana is somewhat green, you can add a bit of water to make it easier to mash.
3. Add up to 10 ml of the extraction buffer to the bag, and mash some more. Again, try not to create excessive bubbles. Remind small children not to taste the fruit after this step.
4. Set up some sort of filtration system. This can be a simple as a coffee filter over a cup or cheesecloth over a funnel. The idea is to separate the fruit juice from the pulpy material. The DNA should now be in the juice that passes through the filter. You can throw away the pulpy remains. The videos have more details about filtering if you have never done it before.
5. Pour your juice into the test tube or spice jar. If you have a lot of bubbles on top, remove these with a medicine dropper. Now slowly pour in 8 to 10 ml of the cold isopropyl alcohol. It should form a layer on the top of the juice.
6. With the wooden stick, stir at the interface of the alcohol and juice. A thick, globby material should form on the stick, which is your DNA. If it doesn't appear right away, give it a minute or two and try again.
There's nothing like being able to watch someone do a demonstration to help you figure out what to do. Here are two videos that show how to extract DNA, each using slightly different techniques.
DNA Extraction from Strawberry Video
DNA Extraction from a Banana Video
These are sure to give you some ideas for further experiments. What happens when you add the alcohol to the test tube first versus second. Does the order change the amount of DNA you obtain?
Once you are confident of your technique, go ahead and try other fruit or vegetables, such as kiwi or onions. You can also compare room temperature versus cold alcohol to see whether it really needs to be cold. Have fun and I'd love to hear what you find out.
For more information about genetics online, try Learn Genetics at The University of Utah.
You Can't Wear These Genes
Reading level: Ages 9-12
Paperback: 48 pages
Publisher: Rourke Publishing (FL) (August 2010)