What you need:
- 3 x clear plastic cups or glasses
- Blue food coloring
- Clear washing up liquid
- 1 tbsp table salt
- 100 ml isopropyl alcohol
- 500ml bottled water
Mix the 500ml water with the salt in a cup or glass. Stir until salt is gone.
Transfer 3 tbsp of the salt water into a separate cup or glass.Gargle the salt water for 1 minute. Spit the water back into the cup.
Add one drop of washing up liquid to the salt water with spit. Stir gently without making bubbles.
In a separate cup or glass, mix the isopropyl alcohol and 3 drops food coloring. Gently pour the food coloring and alcohol mixture into the salt water cup.
Tilt the salt water cup as you pour, so the alcohol mixture forms a layer on top of the salt water. Wait for 2.5 minutes. You should see something white forming.
The white strings are your DNA!
Some of your cheek cells become suspended in the salt water. The washing up liquid breaks down your cell membranes. This causes the DNA to be released into the water.
Other substances from your cheek cells stay dissolved in the salt water layer, but DNA is not soluble in alcohol, so it forms a solid where the alcohol and salt water layers meet.
for a visual explanation: