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Want to see some real DNA?

Maybe even hold it in your hand squish it between your fingers?

With this simple experiment, you can separate the DNA from an onion using supplies you can find in a kitchen. Get an adult to be your lab assistant.

WHAT YOU'LL NEED

THE SCOOP ON DNA

DNA is in every cell of every living thing. Every plant and animal is made of many cells. Inside each cell is a piece of DNA. If you dissolve the cell walls, you can release the DNA .

DNA molecules are long and stringy. A single DNA molecule is too small to see. But if you have enough of them, they will tangle together into a blob big enough to hold in your hand. These clumps of DNA are pale white and feel a little slimy. In this experiment, you will see DNA appear out of nowhere from a clear liquid.

THE MATERIALS

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and adult

a medium-sized onion

a knife & cutting board

a blender

salt

a strainer or sieve

dishwashing liquid or clear shampoo

two clear glasses or empty jars

(each should be 12 oz. or  more)

masking tape and a pen

two spoons and a stick

meat tenderizer

(Meat tenderizer is sold in the spice sections of most supermarkets)

rubbing alcohol

(Rubbing alcohol comes in different strengths. Look for 70% or higher. An adult must  help you with this.)

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THE CONTROL

You really only need one glass to extract DNA from an onion. So why use two?

In the second glass, you'll also put some onion and just  leave it alone. This  glass is called your control. Scientists never do an experiment without having a control for comparison.

Why? Let's say you do your experiment, and when you're done, you see some stuff floating around in the glass. How do you know if it is DNA or just plain old chopped onion? Without a control, it's hard to be sure. A control gives you something to compare. If you use a control, you will know whether you've got DNA or onion in your glass.

WHAT TO DO

SAFETY WARNING

You have an important safety responsibility if you are going to do this experiment.

  • Rubbing alcohol is poisonous. Don't drink your experiment! Make sure you and your lab assistant wash all the kitchen supplies and your hands really well when you're done. And don't let your little brother or sister or dog near it. Rubbing alcohol can make them very sick.
  • Never put your hand inside a blender. The blades can cut your fingers.
  • Don't do this experiment without an adult being there with you the whole time.
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Chop up the onion into chunks and put it in the blender. Your adult lab assistant should do this.

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Add a teaspoon of salt and twice as much water as the onion mixture. Blend for about ten seconds. You should end up with a mushy mixture.

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Label two clear glasses with masking tape. Write "control" on one and "liquid soap and enzymes" on the other.

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Strain the onion slush by pouring it through a sieve or strainer into a mixing bowl or pitcher.

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Fill between one-third and one-half of each glass with the onion juice. Pour the same amount into each.

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Add dishwashing liquid — one-sixth the amount of the onion juice — to the glass labeled "liquid soap and enzymes." (Don't add any to your control.)

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Add a half-teaspoon of meat tenderizer to the glass labeled "liquid soap and enzymes." (Don't add any to your control.)

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Stir gently and wait ten minutes. Don't stir too hard or you'll break the long, fragile DNA molecules. Use a different spoon to stir each glass.

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Slowly (you must do this slowly) pour alcohol into each glass. The amount of alcohol in each glass should equal the amount of mixture in the glass. Don't stir.

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You should see alcohol floating on top of your onion mixture. After a few minutes, stringy globs will appear in it. That's the DNA! You did it!

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Slowly swirl a stick through the alcohol. DNA clumps should stick to it. You can then lift them up for a closer look. Go ahead and touch the DNA—but wash the slimy stuff off your hands afterward!

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What happened in the control? Does it look the same or different?

MORE EXPERIMENTS...

You can do this experiment with other common foods. Try peas, kiwis, broccoli, spinach, chicken liver, and bananas. Then experiment with whatever you want and see what happens! Keep a journal of your experiments.

  • Try using warm water and chilled alcohol. Does this change your results?
  • Strain the onion mixture through a coffee filter instead of a sieve. Does the DNA make it through?
  • Experiment with different amounts of ingredients. Leave some out entirely and see what happens. This is similar to what you did in the control. Will the experiment work without using meat tenderizer? Find out by using three glasses: one with liquid soap only, one with liquid soap and meat tenderizer, and one with neither.

 

This experiment was adapted from procedures developed by the Genetics Science Learning Center at the University of Utah.

Image Credits:

All photos: AMNH