DNA Detectives: Extract your Own DNA

Overview & Concepts

This is an introductory lesson to DNA.  It involves an activity that gives students an opportunity to examine real human DNA they extract from the inside of their mouths.  Through this engaging activity, students will develop an  understanding of DNA as a real, tangible substance.   Students will take notice of how their observations from the investigation are different or consistent with their  preconceived notions of DNA.   After this lesson, students will begin studying the structure of DNA.

Grade Level: 

Concepts Covered: 

Genetics, DNA

Prior Knowledge Required: 

genes, genotype, phenotype

Activity Notes

Days to Teach: 

1 Day (45 minute period)

Materials: 

  • 500 milliliters of drinking-water
  • cooking salt or table salt
  • clear cups or glasses, small
  • chilled rubbing alcohol (Isopropyl alcohol USP 70%)  
  • A few drops of blue food coloring (optional)
  • eyedroppers or spoons
  • clear dishwashing detergent
  • stir-sticks
  • Safety Glasses (optional)

Teaching Tips / Activity Overview: 

Introduction

  • Begin by reminding students what they have been studying (genetics) and that they should understand the relationship between genotypes and phenotypes by now and that they should understand that traits are inherited through genes.
  • Ask students what the genes do (1. carry information. 2.determine heritable characteristics of organisms. 3. replicate). 
  • Ask, "What are genes made of?"; the expected response is "DNA." 
  • Ask students to volunteer to tell the class what DNA is.  Ask "when you hear the term DNA, what images come to mind?  If you could see DNA, what would it look like?" 
  • Instruct students to draw what they think or predict what DNA looks like in their journal.   

Activity

  • Explain to student that they are going to find out firsthand what DNA looks like by extracting some of their own to see.  Before the students begin the DNA Detectives activity, go over the instructions; ask students to volunteer to read steps of the directions aloud to the class.  Have a student volunteer read the warning about the alcohol aloud and demonstrate how to add isopropyl alcohol to the water properly.  Check for student understanding of the procedures.
  • Have students perform the DNA Detectives investigation (see materials and equipment). 
  • After the activity, the give students time to answer the following questions in their notebooks: What do you think of the DNA that you see?  How is it similar to and ifferent from the way you thought it would be?  Ask several students to share their answers with the class and the class will discuss their answers.  

NoteIn step 5 it's very important to add the alcohol very gently, so that the water and the alcohol do not mix.

Assessment: 

During class discussions, the teacher should assess students' perceptions and reactions informally. Journal entries should be read by the teacher at the end of the week to ensure that the students are reflecting insightfully and participating fully.  Students receive points for completed entries that are orderly and perceptive. The teacher should also be checking journals throughout the period.

Extensions: 

  • Show students models or videos of the structure of DNA.
  • Allow students to extract DNA from other items like a strawberry or kiwi. 

Resources: 

Acknowledgements: 

These teacher notes and resources were produced by Melissa Barr. The lab activity was obtained from the Extract Your Own DNA lesson at nature.ca/genome/05/051/0511/0511_e.cfm (site no longer online 11/12).

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