Students explore how dominant and recessive traits are expressed and discover how knowledge of heredity is important to agriculture. Grades 3-5

dominant gene: a gene that can hide the effect of a recessive gene

recessive gene: a gene whose expression can be hidden

trait: observable, physical characteristic obtained through genetic inheritance

When plants and animals reproduce sexually, the traits of their offspring are determined by a combination of genes from each parent. Each parent contributes one-half of the genes for each trait. In the simplest cases, genes are either dominant or recessive. When a dominant gene combines with a recessive gene, the dominant gene’s characteristics are expressed in the offspring. When two recessive genes are combined, the recessive characteristic is expressed in the offspring. Co-dominance occurs when the genes for a particular trait are equally strong. In this case, the two variations of the gene are expressed in equal strength.

Plant breeders use knowledge of dominant and recessive traits to create new varieties of crop plants and ornamental plants. In agriculture there are many examples of dominant, recessive, and co-dominant traits. Some examples are listed below:

• Red potato skin is dominant over white potato skin.
• Russet-colored potato skin is dominant over white potato skin.
• Green peas are dominant over yellow peas.
• Red cherry tomatoes are dominant over yellow cherry tomatoes.
• Red and white snapdragon flowers are co-dominant and produce pink flowers.
• Short and tall corn plants are co-dominant and produce medium height corn plants.
• Tall sunflower plants are dominant over short sunflower plants.
• Yellow-kernel corn is dominant over white-kernel corn.

1. Have students list words that are associated with the terms dominant (dominated, dominating, dominate, domain, dominance, predominant, dominator, etc.) and recessive (recessively, recede, recess, receded, receding, recessional, recession, etc.). 
2. Discuss the difference between dominating a situation and receding from a situation and provide examples. For instance, if two people wanted to climb up the ladder of a slide at the same time, one person might dominate the situation by yelling or pushing the other person out of the way. Another person might recede by walking away and playing somewhere else. The receding person may play at the slide later when there is less competition (similar to recessive genes). Role-play a few situations, such as lining up after recess or participating in class discussions.
3. Ask students if they can think of a connection between these two words (dominant and recessive) and genetics. Allow students to guess and to offer their ideas using their prior knowledge.
4. Explain that in genetics that are some traits that are dominant over others. Today they will be learning about these traits.

Activity 1: Rock, Paper, Scissors

1. Describe the game Rock, Paper, Scissors using the words dominant and recessive. Explain that rock dominates scissors, scissors dominate paper, and paper dominates rock. 
2. Divide students into pairs, and provide each pair with a copy of the Rock, Paper, Scissors Recording Chart.
3. Instruct the students to play Rock, Paper Scissors ten times and record the outcome of each round on the chart. 
4. Discuss the outcomes that students observed. Are there ways of making certain one person will always dominate (win)?
5. Discuss dominant and recessive in terms of genes and heredity.
6. Provide each pair of students with a copy of the Plant Features activity sheet to color and cut out. When finished, ask students to place the features into the prepared gene pool containers (boxes, envelopes, etc.) labeled “Leaves,” “Fruit,” “Flowers,” “Roots,” and “Stems.” 
7. Place the five gene pool containers in different locations throughout the room.
8. Hand out a copy of the What Does It Look Like? activity sheet to each pair of students. 
9. Next, have each individual student randomly select one feature from each of the gene pool containers. 
10. Returning to their pairs, have the students fill in the activity sheet with the features chosen. The partners then need to determine what their plant looks like. For example, if one partner chooses a dominant round fruit and the other partner chooses a recessive oval fruit, the plant will have round fruit. Finally, ask students to draw their plants, showing the appropriate features. 
11. Have the students display their plants. Compare the number of dominant traits expressed to the number of recessive traits expressed. Discuss the wide variety of plants produced from the same gene pool and how this activity shows that it is highly unlikely for two brothers or sisters to have exactly the same genetic makeup.
12. Discuss how knowledge of dominant and recessive traits is important to agriculture. Ask students to think of all the different types of apples (or lettuce, onions, potatoes, etc.) they can buy at the grocery store. Each of these different types was developed by plant breeders who cross different parent plants to get the characteristics they want. 

Alternative Teaching Strategies for Activity 1:

1. Rather than working in pairs, have the class create one plant on a flannel board by randomly selecting from the gene pool.
2. When discussing traits that are dominant, co-dominant, and recessive, use colored markers and a whiteboard to illustrate. Two colors can be blended for co-dominance and a recessive color can be erased.

Activity 2: Mixing Inherited Traits

1. Place the following eight piles of mixed glitter on small paper plates and spread the plates out on a table, leaving at least a foot between plates.
   • Red, blue, and green
   • Red, silver, and green
   • Red, blue, and magenta
   • Red, silver, and magenta
   • Gold, blue, and green
   • Gold, silver, and green
   • Gold, blue, and magenta
   • Gold, silver, and magenta
2. Pass out one Plant Parent 1 Card to each student. Explain that the card represents one parent plant and that each color on the card represents one trait that the parent will pass on to its offspring.
3. Pass out one chenille stem piece to each student. Tell students that they are going to become pollinators. The chenille stems represent the hairy legs of a bee and the glitter piles represent the flowers of second parent plant.
4. Show students how to bend the chenille stems into “bee legs” (a right angle bend near one end).
5. Tell students they will visit one of the eight flowers (glitter piles) that will be the second parent (Parent 2) to the offspring they are creating. 
6. Ask each student to visit and place his or her “bee leg” into one pile of glitter.
7. Have students return to their desks and remove the glitter from the “legs” onto a sheet of paper. Have them identify which colors are present for Parent 2 and compare them to the colors from the Plant Parent 1 Card.
8. Explain that sometimes a trait that an offspring receives from a parent is not visible, even though the offspring carries the information for that trait.
9. Show students the Glitter Plant Trait Key, which lists the trait that the offspring will exhibit for each color (trait) received from Parent 1 and Parent 2.
10. Hand out and ask students to complete the Glittering Offspring activity sheet. They should use the glitter code listed at the top of the Glitter Plant Trait Key: red/gold colors determine the color of the petals; blue/silver colors determine the length of the stem; and green/magenta determine the color of the leaf. 
    • Example: If you had red, silver, and green listed from your Plant Parent 1 Card, and you obtained the colors gold, silver, and magenta from your glitter pile (Parent 2), then your plant would have:
      •  Red and Gold = Red Petal
      • Silver and Silver = Short Stem
      • Green and Magenta = Dark Green Leaves
11. Review with students which colors from the Glitter Plant Trait Key represent dominant traits and which represent recessive traits. Discuss the similarities and differences among the offspring and the frequencies of each visible trait. Discuss the challenges that recessive traits might pose to plant breeders.

After conducting these activities, review and summarize the following key concepts:

• Plant breeders use knowledge of inherited traits to develop new varieties of crop and ornamental plants with improved characteristics.
• Plants and animals that reproduce sexually inherit one-half of their genes from each parent. 
• Dominant genes can hide the expression of recessive genes.

1. https://history.nih.gov/exhibits/nirenberg/HS1_mendel.htm
2. http://www.pollinator.org

Lesson adapted by Utah Agriculture in the Classroom. Activity 2 written by Rose Judd-Murray and Debra Spielmaker.

• Bitter/Sweet Cucumber Taste Test
• DNA Learning Center
• Gregor Mendel: The Friar Who Grew Peas
• How Do Apples Grow?
• How to Extract DNA from Anything Living
• In the Garden with Dr. Carver
• Parent/Offspring Cards
• Pollination Simulation Kit
• Pompom Punnett Square Kit
• Strawberry DNA Necklace