1. Place some onion into some detergent+salt. The detergent breaks down the cell walls and the salt helps the DNA stick together.
2. Put the mixture into a water bath at 60C for 15 minutes. This de-natures the enzymes that could digest the DNA and softens the onion cells.
3. Cool the mixture down in ice to prevent the DNA breaking down.
4. Blend the mixture for a few seconds to break open the cell walls and release (but not break up) the DNA.
5. Cool the mixture down again then filter it to remove the big bits.
6. Gently add ice cold alcohol (eg ethanol) to the mixture. The DNA will come out of the solution as it's not soluble in cold alcohol. It has the appearence of a stringy white substance.
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