Activity 1: Trait Variation

1. Remind students about the similarities and differences among humans that come from inherited traits. Tell them that the class is now going to investigate the amount of variation present in crop plants.
2. Divide students into groups and provide each group with one image from the Row Crop Pictures found in the Essential Files. Ask each group to make a chart of the similarities and differences they can see between plants in the pictures. Discuss how the amount of variation they observe compares to the amount of variation that can be observed in humans. As a class, brainstorm reasons why farmers might not want variation among plants they grow to produce crops.
3. Show each group of students an ear of dried popcorn and an ear of Indian corn. If you do not have ears of corn available, you can use pictures or have students compare all of the popcorn seeds and all of the Indian corn seeds that will be used in Activity 2.
4. Ask each group to make a chart of similarities and differences between the kernels on an ear (each kernel is an individual offspring of the plant that produced the ear). As a class, discuss their observations. Discuss the possible sources of variation (sexual reproduction, open pollination). Also compare the traits of the two corn varieties.
5. Explain to the students that in general, it is easier for farmers to manage uniform crops. For example, most corn is harvested using a machine called a combine. All of the corn is harvested at the same time, so it is best if it all matures at the same time. However, sometimes variation is desirable. Indian corn is used mostly for ornamental purposes, so variation in the color of the kernels is desirable.

Activity 2: Living Corn Necklace

1. Tell the students that they will continue their investigation of corn by observing how corn seeds germinate and begin to grow. They will observe two varieties, Indian corn and popcorn, that have been selected over time for different traits.
2. Provide each student with one popcorn seed and one Indian corn seed. Ask each student to begin their corn journal by drawing a picture of each seed and writing several sentences to describe it.
3. Provide groups with the materials needed for each student to make a “Living Necklace” (plastic jewelry bag, cotton balls, and yarn), permanent marker(s) and a cup of water. Direct students to make their necklaces as follows:
   • Use the permanent marker to label one side of the bag P and the other side I.
   • Dip a cotton ball in water so that it is thoroughly wet but not dripping. Excess water will cause the seeds not to sprout.
   • Place the cotton ball in the small plastic bag.
   • Put one popcorn seed on the side of the cotton ball facing the label P.
   • Put one Indian corn seed on the other side of the cotton ball, facing the label I. The labels will help students remember which seed is which.
   • Seal the bag. String the yarn through the hole in the jewelry bag. Tie a knot in the end of the string to form a necklace.
   • Bags can be hung from tacks on a bulletin board and taken down for student observations.

   • Teaching Tip: The corn seeds will sprout in three to six days. Starting on a Friday and making the first observations on Monday will speed up this activity.

     

4. For one week have students record in their journals the changes they observe in their seeds, including information about observable traits such as: number of days from “planting” until the root and the shoot can be seen; root and shoot lengths and color; and number of leaves and roots.
   • Use hand lenses to observe the roots and shoots as they emerge and grow.
   • Use rulers to measure the length of roots and leaves as they grow.
   • Teaching Tip: It is difficult to take the seedlings out of the bags and get them back in without breaking the roots. Ask students to measure through the bag instead. The roots will curl, so you may want to suggest measuring them in sections and estimating as necessary.
5. In small groups, have students make charts or graphs of the data they collected for measurable traits (leaf and root length). Ask them to look for differences between the popcorn and Indian corn.
6. As a class, discuss how each group compared their data for popcorn and Indian corn. Which kinds of charts or graphs worked the best? Were there noticeable differences between the popcorn and Indian corn seedlings?
7. Discuss how plant breeders control inheritance and work to develop seeds that will reliably express desired traits. Popcorn has been selected for different traits than Indian corn.
8. Compare the traits of the corn seedlings to those of mature corn plants (using photographs).
9. Use the We’re Expecting... activity sheet to review the difference between cross-pollination and self-pollination and to introduce the concept of dominant and recessive traits.