Have students set this test tube aside and continue to Part 2. Have students pour the liquid into a test tube and add 5 ml of cold isopropyl alcohol. Students should place plastic wrap tightly over the top of the test tube, and slowly turn it upside-down and back again. They should be able to see the white mucus-like DNA form. If needed, have students gently tilt the test tube several more times until they see the DNA precipitate.
Extension Have students draw out the threads of DNA from the onion cell and herring sperm.
To do this, supply each group with a pipette that has one end melted to form a small hook. Have students follow the instructions for extracting and isolating the DNA up to Step 5. Then have students gently pour the alcohol down the sides of the test tube. Ask students to use the pipette hook to gently tease out a thread of DNA from the interface between the alcohol and the liquid in the test tube.