Free 8th Grade Dihybrid Cross Lesson Plan (Science)

Topic: Mendelian genetics

Objectives & Outcomes

• Understand the concept of a dihybrid cross and how it can be used to study the inheritance of two contrasting traits.

Materials

• Tomato plant with contrasting seed pods (e.g. unripe vs. ripe)
• Seeds from a red and a green pea plant
• Seed germinator
• Small plastic cups or containers for growing the seeds
• Marker or pen for labeling the plants

Warm-up

• Show the students a tomato plant with red unripe seeds and a tomato plant with green ripe seeds. Ask them to comment on the differences they observe between the two plants.
• Introduce the concept of genetic inheritance and explain that all living organisms have genes that determine their physical and behavioral characteristics.
• Ask the students to think of a pair of traits that they have seen in animals or plants and that are inherited from parent to offspring.

Direct Instruction

• Review the process of cross-pollination and explain that it is the process by which pollen from one plant or flower is transferred to the ovary of a different plant or flower, resulting in the fertilization of an ovule and the formation of a seed.
• Explain that dihybrid crosses are the most common type of cross used to study the inheritance of two traits in organisms.
• Define the terms "dominant" and "recessive" and give examples of each.
• Explain the steps involved in conducting a dihybrid cross and explain how the results can be used to determine the percentage of each trait present in the offspring.

Guided Practice

• Have students work in pairs to conduct a dihybrid cross using the seeds and plants provided.
• Have students follow the steps outlined above to conduct the cross and record the results.
• Have students use the results to determine the percentage of each trait present in the offspring.
• Have students discuss and explain their results.

Independent Practice

• Have students choose a different trait that is expressed in pea plants (e.g. flower color, leaf size) and conduct a dihybrid cross to determine the percentage of each trait present in the offspring.
• Have students repeat this process with a different trait to confirm their results.
• Have students create a presentation or poster to communicate their results and any observations they made during the experiment.

Closure

• Review the steps of a dihybrid cross and the expected results.
• Ask students to share their presentations or posters and discuss what they learned about Mendelian genetics.

Assessment

• Observe students during the independent practice activity and provide feedback on their understanding of Mendelian genetics.
• Evaluate the group presentations or posters and provide feedback on the students' ability to communicate their understanding of the topic.