Comparing DNA yield across fruits

Where to buy & price

Just examples of where to look and roughly what to expect to pay, get everything from wherever works for you, at whatever price you find.

Strawberries/bananas, Naivas, Quickmart, Chandarana, or any open-air market, bananas ~KSh 10–20 each, strawberries ~KSh 150–300/punnet, buy two different fruits for this comparison. Dish soap ~KSh 100–150. Table salt ~KSh 30–50/500g. Rubbing alcohol/surgical spirit, Goodlife Pharmacy, MYDAWA, Carrefour, Nila Pharmaceuticals (100ml Rosapharm surgical spirit sold at Carrefour Kenya; 5L container KSh 999 at Tiba Quip Africa, buy the smallest size available, you'll need enough for two extractions).

Cold storage / timing

Freeze the rubbing alcohol for 10–15 minutes before use for both extractions, a real requirement, not optional (NIH's genome.gov: "the colder the rubbing alcohol, the less soluble the DNA will be in it").

Reagents & materials required

Procedure, step by step

1. 1

   Set up two identical extraction stations side by side, one for strawberry (or another high-ploidy fruit) and one for banana or kiwi.

2. 2

   Place your first fruit in a ziplock bag and mash it thoroughly by hand for 1–2 minutes until smooth, repeat separately for the second fruit in its own bag.

3. 3

   Mix an extraction buffer: 2 tablespoons dish soap, 1 teaspoon salt, and 1 cup water, stirred gently. Make two batches, one for each fruit.

4. 4

   Add 2–3 tablespoons of the extraction buffer to each mashed fruit, reseal each bag, and mash gently for another minute to mix.

5. 5

   Filter each mixture separately through its own coffee filter or cheesecloth into its own clear cup or tube, collecting only the liquid.

6. 6

   Tilt each tube and slowly pour cold rubbing alcohol down the inside wall of each, forming a separate layer on top of each fruit extract, use roughly equal volumes of alcohol to extract for both.

7. 7

   Let both tubes sit undisturbed for the same amount of time, at least 2–3 minutes, watching for white, stringy DNA precipitate forming at the boundary in each.

8. 8

   Compare the amount of visible DNA precipitate between the two tubes side by side, more precipitate generally reflects more DNA per unit of cell mass.

9. 9

   Photograph both tubes together in the same shot so the difference is easy to see, and record which fruit produced more.