View Learn.Genetics Materials

Genes, Traits & Change over Time

Unit Overview

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!

Image Files

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

Notes from the Developers

A word about phenomena

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

What about worksheets?

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.

Suggested Lesson Sequence


How are traits made?
  • 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.
Ideas for introducing this module:
Class TimeActivityDescription
10 minTraits: Two Models (pdf)How are traits made? Students weigh in on two different models.
10-15 minHow Traits are Made (video)This video introduces traits and describes how they are shaped by both genes and the environment.
20-30 minWays Proteins Make You (explore)Through 12 examples, this interactive slideshow focuses on proteins and how they work together to make traits.
25-35 min Trait Shuffle (pdf)Students consider examples of traits that vary (12 from animals, 12 from plants). Then they sort them by whether they think the differences are caused mostly by genes or the environment.
30-40 min Traits: Weigh the Evidence (pdf)Students revisit the two models presented at the beginning of the module. They consider how four lines of evidence relate to each model and explain why they think one is correct.
Optional related activities:

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


How are traits passed down?
  • 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.
Ideas for introducing this module:

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?
Notes from the Developers:

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.

Class TimeActivityDescription
10 minHow Genes Are Inherited (video)This video shows how genes—as both physical objects and coded information—pass from parents to offspring during sexual and asexual reproduction.
15 minReproduction & Variation (explore)This animated slideshow steps through the two sources of genetic variation: recombination (gene shuffling) and mutation.
30-45 minMake-a-Model (pdf)Students make models of asexual and sexual reproduction that include mutation, focusing on the sources of variation in each types.
25-35 minMutt Mixer (interactive explore)Students play with dog traits and see how two parents can make greatly varied offspring. Built-in achievements reveal even more about inheritance.
30-40 minMutt Mixer Modeling (pdf)Using cut-outs based on Mutt Mixer art, students model how an individual can make reproductive cells with different combinations of alleles. Students can then combine their dog’s reproductive cells with others' to make offspring.
30-40 minOptional: Cup-a-Genes (pdf)Students use manipulatives to model how alleles are inherited during sexual reproduction.
25-35 minHeritable or Acquired? (pdf)Students learn about a population of organisms with a trait that varies (8 tricky examples are provided). They analyze data about the organisms' offspring to decide whether the differences are inherited or acquired.
Optional related activities:

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.

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

Reproductive Success

How do traits affect an individual's chances of surviving and reproducing?
  • 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.
Notes from the Developers:

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.

Ideas for introducing this module:

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

Class TimeActivityDescription
30-40 minHelpful, Harmful, or Neutral? (pdf)Students learn about a population of organisms where a trait varies (4 examples are included). Then they evaluate the trait variation in two different environments, deciding if it will be helpful, harmful, or neutral to the organism.
20-30 minGenetic Survivor (explore or pdf)Students inventory 5 of their traits then imagine how they might fare in an apocalyptic future with threats like tongue parasites or killer grandmas.
10-15 minChoose the Best Explanation (pdf)Students review key concepts from the last two modules, helping to solidify the connections between gene variations, trait variations, and reproductive success.

Natural Selection

How do populations change over time?
  • 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.
Ideas for introducing this module:

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.

Notes from the developers:

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.
Class TimeActivityDescription
10-20 min Rock Pocket Mouse SimulationThis simulation, based on the rock pocket mouse, shows how the traits in a population can shift over time through differences in reproduction and predation.
5-10 minNatural Selection: Three Models (pdf)How does natural selection work? Students weigh in on three different models.
15-25 minShape Shifters (interactive explore)Don’t spoil the surprise! Without knowing that they’re participating in a natural selection simulation, students build stacks of colored shapes and submit them to a “judge.” A big reveal at the end lets them in on what’s really been going on.
15 minHow Natural Selection Works (video)This video introduces natural selection, preparing students to evaluate the examples in the next activity.
45-60 minCSI: Changing Species Investigation (pdf)Lots of species change over time, but it’s not always due to natural selection. Students evaluate data about a population (4 examples are provided) and work together to decide where natural selection is at work and where it isn’t.
50-60 minNatural Selection: Weigh the Evidence (pdf)Students revisit the three models presented at the beginning of the module. They consider how several lines of evidence relate to each model and explain why they think one is correct.
70-90 minMythUnderstood (pdf)Students read illustrated tall tales (4 are provided) about how certain animals got their traits. They identify the myths in the stories then write a more accurate version of what could have happened.

About this Unit

This project is funded by the National Science Foundation, grant #1814194. Any opinions, findings, and conclusions or recommendations expressed in these materials are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.