Darwin and DNA

12 02 2010
Today is Charles Darwin’s birthday.  Darwin was born in 1809 and discovered that living things adapt to their environment in a process called natural selection. Natural selection can take a long time, but eventually these plants and animals evolve and keep certain traits so they can survive longer in their environment.

DNA is contained in the cells of every living thing, and it’s the code that makes every living thing unique. When plants and animals evolve, they do so through changes in this special code. It’s amazing that Charles Darwin was able to develop his theory of natural selection without even knowing about DNA and how it works!

In this activity from the New York Hall of Science you can extract the DNA of a strawberry.

Supplies:

1 large glass
1 small glass
measuring spoons
9 tbsp water
1/4 plus 1/8 tsp salt
1 coffee filter
2 tsp dishwashing liquid
rubbing alcohol, at least 70%
1 sealable sandwich baggie
1 wooden coffee stirrer or toothpick
1 strawberry with the top taken off

Instructions:

The extraction buffer.

1. Make an extraction buffer by mixing together the dishwashing liquid,
water and salt in the small glass.

To be able to see the DNA of the
strawberry you have to use an
extraction buffer to break open the cells. The buffer includes soap and salt. The soap breaks apart fat layers of the cell membrane. The salt makes the contents of the cell to come out through  a process called osmosis. The contents inside the cell with a lower salt concentration rush out of the cell to a higher salt concentration.

2. Place your strawberry in your bag and squeeze all the air out of the bag and close it properly.

3. Squash the strawberry in the bag. Then open the bag and add 3 teaspoons of the buffer. Close the bag, squeezing the air out again.  Keep squashing the strawberry and the buffer.

The strawberry and buffer squashed.

4. Strain the mixture into the large glass by using the coffee filter. Wrap the filter closed and gently squeeze the contents against the side of the glass to get the liquid into the glass. Make sure the coffee filter doesn’t rip.  The filter helps separate the cellulose and bigger components of your contents from the DNA in the liquid.

5. Tilt your glass to increase the surface area and  very slowly add the rubbing alcohol. Slowly rock the glass back and forth as you are doing this. Pour until there is a layer 1/2 inch deep on the top of the water.

Pour the alcohol slowly so the DNA can properly be extracted.

6. Let the glass sit for a minute. You should see three layers. One is reddish and contains water with proteins, the middle layer is whitish, and the upper layer is clear (the rubbing alcohol has the lowest density so it goes to the top).

Your mixture should look like this after you pour in the alcohol.

7. Look for the white cobwebs or clumps in your glass resembling mucus, they should be in the middle layer.  This is your strawberry DNA! Take your coffee stirrer or toothpick and stick it into the glass. Twirl the stick until DNA attaches to it.

Strawberry DNA!

For more cool experiments like this, check out the New York Hall of Science’s website here.

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