Genes, Traits & Change over Time

This 4–5 week, NGSS-friendly unit integrates core ideas in genetics, heredity, and natural selection. The unit focuses on the mechanisms that drive genetic variation and how natural selection makes certain trait variations more common in a group. Its easy-to-implement multimedia and paper-based activities are paired with scaffolded practice in working with models, crafting explanations, and identifying cause and effect relationships.

• Three-dimensional
• US Middle School level (ages 12–14)
• Flexible: use in sequence as a complete unit or integrate with other curriculum materials
• Consistent visual language: structures are depicted similarly throughout
• Teacher supports, including suggested implementation, pitfalls to watch for, and background information

Click here for an eLearning module designed to walk you through the unit. It's like a curriculum workshop that you can peruse at your own pace!

We offer some graphics from the unit's print-based materials as image files. You can download activity-specific bundles of images as ZIP files and use them with your favorite tools. Plug them into digital whiteboards (like Jamboard), slides, documents—anywhere you can drop a jpeg file!

Genes, Traits & Change Over Time Image Files

Phenomena are observable events that we can use science knowledge to explain. Their use can shift us from learning about something, to figuring out why or how something happens. Phenomena can be used in three ways:

• Anchoring, as a focus for the unit;
• Investigative, as a focus of an instructional sequence or lesson;
• Everyday, to connect anchoring or investigative phenomena to student experiences.

You will see investigative phenomena incorporated in the unit’s materials. If you are looking for other phenomena to use in this unit, here are some ideas to get you started.

NGSS Phenomena and Outside Resources

The unit’s worksheets focus on building the science practices of Constructing an Explanation and Working with Models, for the most part. You may wish to create your own focus questions, graphic organizers, note catchers, etc., for any activity you see fit. Teacher choice!

Look for more notes from the developers spread throughout the unit’s pages.

• Traits are made by multiple genes working together plus factors from the environment.
• Genes code for proteins; teams of proteins build the body and make it work.

• Project images of two or more individuals of the same species, each with visibly different traits. Discuss similarities and differences. Here are some examples:
  • Dog Traits
  • Dalmatian Traits
• Take an inventory of traits in the classroom with one of these simple activities:
  • An Inventory of My Traits (for more information about the featured traits, see Observable Human Characteristics)
  • A Tree of Genetic Traits
• Generate a whole-class list of trait examples. Work toward building a consensus definition of “trait.”

These activities explore transcription and translation. If you cover this topic, we suggest plugging it after Ways Proteins Make You.

• How a firefly's tail Makes Light (video) — This video lays out the steps between a gene and a trait.
• Transcribe and Translate a Gene (interactive) — Insert, delete, and remove bases from a DNA sequence, and see how the changes affect the mRNA and protein that are made from it.

• Genes, and the traits they make, pass from parents to offspring through reproduction.
• Mutation and allele shuffling during reproduction contribute to genetic, and trait, variation.

Remind students of the final understandings from the previous module (Traits):

• Traits are made by multiple genes working together plus factors from the environment.
• Genes code for proteins; teams of proteins build the body and make it work.

Get a read on what your students already know about inheritance by discussing the following:

• How are traits passed down?
• Do you inherit traits from aunts and uncles? grandparents?
• Are offspring identical to parents?

The focus here is on how and where variation is generated in asexual and sexual reproduction and not on the mechanics of each type of reproduction (e.g., mitosis and meiosis). This focus on variation is important for framing the role of inheritance in natural selection.

Here are some activities you could use if you want to spend more time on mutation and sexual/asexual reproduction. You can work them into the sequence or not—your choice.

• What Is Mutation? (video) — This intro-level video covers the basics of mutation.
• Mutate a Gene (interactive) — This interactive could be useful if you have already covered transcription and translation.
• Sexual vs. Asexual Reproduction (interactive) — This simple interactive features diverse organisms that reproduce in various ways.

For teachers whose schools, districts, or states require them to provide instruction on Mendelian inheritance and Punnett squares, we offer the following:

• Practice with Punnett Squares
• Complex Traits: Beyond the Punnett Square is designed as a bridge between simple Mendelian inheritance and complex traits involving multiple genes plus environmental factors.

• Some trait variations make an individual more likely to survive and reproduce.
• Whether a trait is helpful, harmful, or neutral to an organism depends on its environment.

This module moves toward thinking about how traits affect reproduction, but it is still focused on traits at the individual level. It helps to lay the foundation for the shift to population-level thinking that comes with natural selection.

Review the final understandings from the previous module, and talk about the question you’ll be exploring for this one.

• In natural selection, inherited traits that favor reproduction are passed down. Over many generations, those traits become more common while traits that do not favor reproduction become less common.

Students have explored examples of artificial selection in Mutt Mixer. Introduce natural selection (another process through which the traits in a group of living things can shift over time). Then use the earlier examples as a springboard to discuss similarities and differences between artificial and natural selection.

Throughout this module, it is important to emphasize the following:

• A shift in focus from the traits of individuals to trait frequencies in populations.
• The introduction of time. Changes in trait frequencies happen over many generations.