Final answer:
In the final step of DNA extraction, adding ice-cold ethanol leads to DNA precipitation because DNA is not soluble in ethanol. As a result, the DNA becomes visible as white strands that can be collected.
Step-by-step explanation:
When ice-cold ethanol or isopropanol is added to the strawberry extract, the DNA precipitates out of solution. This occurs because DNA is soluble in water but not in ethanol.
When the ethanol is added, it changes the solubility conditions for the DNA, causing it to clump together and form white precipitate that can be seen and collected.
This white, viscous material is the DNA which can then be gathered using a glass rod.