Teaching Tips / Activity Overview:
- 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.
- 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.