Lesson: Mice Rule! (or Not)

Contributed by: Engineering K-PhD Program, Pratt School of Engineering, Duke University

A photograph of two brown mice.
Mice!

Summary

Students explore the relationships between genetics, biodiversity and evolution through a simple activity involving hypothetical wild mouse populations. First, students toss coins to determine what traits a set of mouse parents possesses, such as fur color, body size, heat tolerance and running speed. Next, they use coin tossing to determine the traits a mouse pup born to these parents possesses. These physical features are then compared to features that would be most adaptive in several different environmental conditions. Finally, students consider what would happen to the mouse offspring if those environmental conditions were to change. Which mice would be most likely to survive and produce the next generation?
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Probability and statistics are just a few of the tools used in engineering. This lesson explores concepts studied by genetic scientists as well as biomedical and environmental engineers.

Pre-Req Knowledge

An understanding of simple Mendelian inheritance, including concepts of dominant and recessive genes.

An understanding of the concept of adaptation is helpful but is not essential.

Learning Objectives

After this lesson, students should be able to:

  • Explain what is meant by "biodiversity."
  • Explain how adaptive features are maintained in a population of organisms.
  • Apply probability to the study of genetics.

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Middle School Activity
The Benefits of Biodiversity

Students toss coins to determine what traits a set of mouse parents possess, such as fur color, body size, heat tolerance, and running speed. Then they use coin tossing to determine the traits a mouse pup born to these parents possesses.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Find probabilities of compound events using organized lists, tables, tree diagrams, and simulation. (Grade 7) Details... View more aligned curriculum... Do you agree with this alignment?
  • Develop a probability model and use it to find probabilities of events. Compare probabilities from a model to observed frequencies; if the agreement is not good, explain possible sources of the discrepancy. (Grade 7) Details... View more aligned curriculum... Do you agree with this alignment?
  • Recognize and explain the concepts of conditional probability and independence in everyday language and everyday situations. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Understand that two events A and B are independent if the probability of A and B occurring together is the product of their probabilities, and use this characterization to determine if they are independent. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Brainstorming is a group problem-solving design process in which each person in the group presents his or her ideas in an open forum. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Understand the relationship of the mechanisms of cellular reproduction, patterns of inheritance and external factors to potential variation among offspring. (Grade 7) Details... View more aligned curriculum... Do you agree with this alignment?
  • Understand how the environment, and/or the interaction of alleles, influences the expression of genetic traits. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Explain how the environment can influence the expression of genetic traits. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Explain how traits are determined by the structure and function of DNA. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Introduction/Motivation

Ask students what they think of when they hear the word "diversity." After allowing a few minutes for them to share their ideas, point out that there are many contexts in which the word is used. Then ask them what they think is meant by the term "biodiversity." They shouldn't have any trouble realizing that it refers to diversity in a biological context.

Point out two ways to think about biodiversity. One way is the many diverse types of organisms. For example, mushrooms, vegetables, giraffes, whales, spiders, mosses and bacteria all vary tremendously in their structures, body functions and behavior. No one knows how many different species of organisms exist on Earth, but the number is in the millions. Moreover, millions more lived in the past and became extinct. Presently more than 21,000 different species of fish exist, and more than 800,000 species of insects.

Another way to think about biodiversity is the diversity that occurs within a species. As an example, ask students how many different breeds of dogs they can name. Ask how many humans they know that look and behave exactly alike. Even identical twins can be distinguished one from the other by parents and friends.

Next, ask where human babies come from -- that should get their attention! In the unlikely event that they are unclear about this, point out that babies are the result of sexual reproduction. This means that a sperm cell from the father and an egg cell inside the mother combine into one cell, an embryo, in the process of fertilization. Point out that not only humans, but most other animals and plants reproduce sexually. (In plants it is pollen that takes the place of sperm.)

Finally, ask students why the girls in the class do not all look exactly like their mothers, and the boys do not look exactly like their fathers. They should already be aware that they each obtained half of their genes from the mothers and half of their genes from the fathers. Thus, they share characteristics of each of their parents, whose own characteristics are a mixing of their parents' characteristics, etc.

By now, students should be able to explain why so much diversity exists among humans. Point out that similar amounts of diversity exist among plant species and other species of animals, even if to our eyes they look very similar to each other.

Lesson Background and Concepts for Teachers

This lesson and the associated activity are designed to help students understand the theory of evolution by natural selection, as put forward by Charles Darwin. Below is an outline of this theory, modified from a similar outline developed by ecologist Robert Ricklefs. The left column states the theory in the general terms a biologist would use, and the right column gives a specific example that is easily understood by laypersons.

Darwin's table of natural selection. The biologist says: The reproductive protential of populations is great, but populations tend to remain constant in size because populations suffer high mortality. Individuals vry with populations, leading to different survival of individuals. Traits of individuals are inherited by their offspring. The composition of the population graduatlly changes by the elimination of unfit individuials. The layperson says: Mice are capable of producing many babies, so they should cover the Earth, but they don't because many are eaten by predators. Some mice are able to run faster than others, and escape from predators, so do their young. Populations of mice, as a whole, tend to run faster than their predecessors.

Evolution by natural selection would not be possible if there was no variation among individuals in a population, because without variation, there would be no varieties from which to choose. Thus, environmental conditions, which can include climatic factors, food availability, the presence of predators, etc., favor those individuals with adaptive combinations of genes. Those individuals survive to adulthood and reproduce, passing some of their favorable genes on to their offspring. Meanwhile, those individuals with undesirable, i.e., non-adaptive combinations of genes, are selected out of the population before they are able to reproduce.

The associated activity is called The Benefits of Biodiversity because it is intended to let students make the connection between genetic variability and long-term survival of a population. If environmental conditions change, many individuals that were previously well-adapted may no longer be well-adapted. However, if variation exists within the population, others will be. These will be the individuals that leave offspring to the next generation. This idea lays the foundation for understanding how a new species can evolve from an old one.

To further explore the probabilities associated with genetics, Punnett squares (derived from Mendel's theory of genetic visualization) allow one to see what is expected to occur when two sets of genes combine. In the following figure, we have two parents, each with the gene Ff. Capital letters are used to represent dominant genes, while lower-case letter represent recessive genes. Ask the class what the difference is between the two (Answer: Dominant genes are expressed if they are within the genotype at all (FF, or Ff), while recessive genes require that the genotype be completely the recessive trait (ff)).

Using this combination of genes, where each parent has freckles (the dominant trait), but also have the recessive allele, there is a 25% of the child having FF genotype (freckles), a 50% chance of the child having Ff genotype (freckles, with recessive allele present), and a 25% chance of the child having no freckles (recessive).

Punnett square.
copyright
Copyright © U.S. National Library of Medicine http://www.nlm.nih.gov/

Now, using a different combination of parents, where one parent has a homogenous genotype with freckles (FF), and one parent has a homogeneous recessive genotype (ff), there is 100% chance of the child having freckles (with a recessive allele), due to the presence of the F (dominant) allele. This is shown in the following figure.

Punnett square.
copyright
Copyright © U.S. National Library of Medicine http://www.nlm.nih.gov/

Body of Lesson

At this point, change the subject of the lesson to mice. Tell students that rats and mice are examples of mammals known as rodents, along with hamsters, guinea pigs, squirrels, prairie dogs, beavers, and porcupines. Of the rodents, mice and rats represent the largest number of the species. They live in all types of habitats -- forests, fields, swamps, tundras, and even deserts.

Explain that like humans, mice use sexual reproduction, but mice are very efficient at it. A single pair can mate every few weeks and give birth to 5-6 pups at a time. Ask the students, "Why, then, isn't the world covered with mice?" Or more specifically, ask them what reasons they can think of that would cause a young mouse to not survive.

Students should be able to respond that some might get eaten by predators, such as owls, snakes, or cats. Others might not be able to get enough food, or die from disease, or freeze during the winter if they couldn't find a sheltered place to live.

Point out that those that survived had good combinations of physical features that helped them survive to adulthood. We call these features adaptations. Then ask students how these surviving mice got the adaptations they have. The desired response is that the surviving mice inherited their adaptations from their parents, through the genes that were passed on from parents to offspring.

Vocabulary/Definitions

adaptation: A genetically inherited characteristic that enhances the ability of an organism to survive in its environment.

Associated Activities

  • The Benefits of Biodiversity - Students toss coins to determine traits of mice and their offspring, and discuss which features would be most adaptive in several different environmental conditions.

Lesson Closure

Ask students to think about what might happen if the environment a mouse pup was born in suddenly changed. For example, what might happen if a prolonged drought struck an area that was normally wet and lush with vegetation? Would all the mice die? Could they move to a new area several hundred miles away and out of the drought? Let students think about these questions, and some may want to share their ideas. However, instead of commenting on their responses, tell students that they will conduct an activity so that they can see for themselves what might happen in such a scenario.

Assessment

Ask students to define: 1) biodiversityy and 2) adaptation.

References

Ricklefs, Robert E., 1979. Ecology, 2nd Edition, Chiron Press

Contributors

Mary R. Hebrank, project and lesson/activity consultant

Copyright

© 2013 by Regents of the University of Colorado; original © 2004 Duke University

Supporting Program

Engineering K-PhD Program, Pratt School of Engineering, Duke University

Acknowledgements

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: August 22, 2017

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