Strawberry DNA extraction

In this lesson for grade seven, students extract DNA from a strawberry and discuss careers related to genetics.

A lesson plan for grade 7 Science

By Michelle Arias · Adapted by Mitzi Talbert

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CareerStart lessons: Grade seven

This collection of lessons aligns the seventh grade curriculum in math, science, English language arts, and social studies with potential career opportunities.

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• Learn more about DNA, careers, forensic scientists, and science.

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Learning outcomes

Students will learn about the process of DNA extraction and will gain an understanding of how scientists use DNA.

Teacher preparation

Time required for lesson

One to two class periods (45-55 minutes)

Materials needed

• Computer with internet access
• Student handouts:
  • Strawberry DNA extraction directions — one copy for each student
  • “Search for Answers” worksheet — one copy for each student
• One heavy-duty zip-lock baggie
• One strawberry (fresh or frozen and thawed)
• Cheesecloth or coffee filter
• Funnel
• Test tube
• Glass rod or pipette
• One dram container (optional)
• Reagents:
  • DNA extraction buffer: 50 ml liquid dishwashing detergent (Ivory), 15 g NaCl, and 950 ml water
  • Ice-cold 95% ethanol or 95% isopropyl alcohol

Activities

1. Ask the students to explain DNA. What role does it play in our bodies, in plants, and in animals? (DNA is the genetic code that makes up everything that we are.)
2. Ask students to brainstorm what careers would use DNA in their profession. (genetic counselors, OBGYN, forensic scientists, etc.)
3. Hand out the strawberry DNA extraction directions and walk students through the process of extracting DNA from a strawberry. The following directions are on the student handout:
   1. Place one strawberry in a zip-lock baggie.
   2. Smash strawberry with fist for 2 minutes.
   3. Add 10 ml extraction buffer to the bag.
   4. Smash again for one minute.
   5. Filter through cheesecloth or coffee filter in a funnel into test tube.
   6. Holding test tube at an angle, slowly pour the ice-cold alcohol into the tube until the test tube is half full.
   7. At the interface, you will see the DNA precipitate out of solution and float to the top.
   8. You may spool the DNA on your glass rod or pipette tip.
   9. Fill 1 dram container ½ full with ethanol or isopropyl alcohol.
   10. Dip glass rod or pipette tip containing DNA into the 1 dram container and cap.
4. Put students into pairs. Hand out the “Search for Answers” worksheet and have students reseach forensic scientists in their pairs.