1. Have students explore the Journey into DNA in pairs. When pairs are finished, discuss the meaning of each section as well as any questions students have during the activity. When finished, discuss the following:

• Inside what structure are the cell's chromosomes found?
• How many chromosomes are there in nearly every one of your body's cells?
• What is the shape of the DNA molecule?
• How many different types of bases are there in a molecule of DNA?

2. Have students watch the Human Genome Project video and discuss the following:

• What is DNA?
• Where is DNA found?
• In what way does DNA provide the code of life?
• What are the four letters in a DNA molecule, and what do they represent?

3. Divide the class into groups of three or four students. Give each group a copy of the nucleotide schematic and the licorice, toothpicks, and gumdrops. Tell each group to study the picture, making note of the following:

• the parts of a nucleotide
• that a DNA molecule is made up of thousands and thousands of nucleotides
• how bases pair up: adenine with thymine (AT, TA), and guanine with cytosine (CG, GC)

4. Tell students that they are going to build models of the DNA molecule, each five nucleotides long, using the materials you have given them. In other words, they're building the equivalent of genes. Remind students that, while the order of nucleotides could be critically important in a real gene, they should not be concerned about the order of their nucleotides, as long as the bases are paired correctly (see above). Write the following key on the board. Ask students to refer to the key when constructing their models.

Key

• Licorice = phosphate "backbone" of the DNA molecule
• Short sections of toothpicks = sugar that connects the phosphate to the base
• Gumdrops = bases (red = A; orange = T; green = C; yellow = G

5. Have the groups begin producing their models, as follows: Each model should consist of two strands of licorice, with five gumdrops attached to each strand. Tell students to use short sections of toothpick to attach the gumdrops to the strands at equal intervals. Because each color gumdrop represents a different base, the gumdrops on one strand must correspond to the appropriate gumdrops on the opposite strand. For example, a red gumdrop always pairs with an orange gumdrop, while a green gumdrop always pairs with a yellow gumdrop. Instruct students to attach the gumdrop base pairs with pieces of toothpick. The resulting model can be handled carefully without it falling apart.

6. Have students write down the base pairs of their model molecules. Each group will probably have a different sequence of base pairs for each molecule. Some examples are listed below.

Molecule 1

Molecule 2

7. Write each group's base-pair sequences on the board. When finished, you will have the sequence for the entire class. Remind students that the class sequence is only a tiny fraction of most real DNA molecule sequences.

8. Have groups connect their DNA segments to form a giant model DNA molecule.

9. Have students watch the Gene Control and Genetic Tool Kit videos and discuss the following:

• What types of things do genes control in a developing organism?
• What are master control genes and how do they function?
• What does the master control gene called the "eyeless gene" control? What happens when it is removed or damaged?
• What happened when the eyeless gene was transferred from a mouse to a fly?
• Where does an individual organism get the genes it has?
• Can an individual organism change the sequence of its genes during its lifetime?
• How are the traits of an organism related to its DNA sequence?
• What would happen if there was a "mistake" in the DNA sequence?