Genetic Variation and Natural Selection

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Objective

SWBAT construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.

Big Idea

Impact of Genetic Variation on natural selection

Engage

10 minutes

You have been learning that animals develop adaptations over time that allow them to survive in harsh environments. The elephant cools its blood by flapping its ears; a rhino has its thick skin to protect it from thorns; a zebra travels in a herd and has stripes so that individuals are hard to hunt. You are going to design your own animal with an adaptation.

The purpose of this activity is for students to begin to think about how genetic diversity allows for certain individuals to have a greater probability of survival and reproducing in a specific environment.(MS-LS4-4. Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.) 

Directions:

Pick ONE of the challenges below and come up with an animal that has 3 adaptations to help it compensate for the problem. Your adaptation should be a natural type of adaptation - no strapping a flashlight to the head of the animal so that it can see better at night!  You must complete an annotated illustration of your animal's 3 adaptations.

Animal A:  A yellow and orange clown fish lives in dark green tropical coral. It needs some protection from larger fish that prey on it.  Its major food source is dying off and new food sources live in deeper, colder waters. Other small fish at this water level tend to swim faster than this clown fish can swim.

Animal B:  A small mammal living in the forest has trouble finding food at night. It hides during the day. It has yellow fur and is hunted easily by 3 different species of predators in its environment.  

Explore

25 minutes

Now students complete a Variation and Selection Activity (the famous Egyptian Origami Bird, by the University of Indiana). (SP2 Developing and Using Models

In this activity, students are able to explore how only birds which can fly long distances (genetic diversity) between sparsely spaced oases will be able to live long enough to breed successfully. Another concept that Variation and Selection Activity addresses is the impact of genetic mutations on the structure and function of an organisms. (MS-LS3-1. Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism/CCC - Cause and Effect).  

Students are able to visually see how natural selection may lead to increases and decreases of specific traits in populations over time. 

Materials needed to construct the Egyptian Origami Bird (below):

  

  • Paper
  • Tape
  • Straws
  • Scissors
  • Coin
  • Six-sided die 

Explain

10 minutes

In this section of lesson I show students the Natural Selection = Mechanism for Survival video on genetic variation by the California Academy of Sciences. (I show the video up to minute 7:15 for the purpose of this lesson.)

As students watch video they answer the following questions:

  1. What is the source of the genetic variation in natural selection?
  2. Do individuals within a species vary? Give an example of one variation. 
  3. What are mutations? How do they affect genetic variation?
  4. What are the 3 sources of mutations?
  5. What are alleles? Give an example.
  6. How doe alleles get distributed to offspring?
  7. What does genetically unique mean?
  8. Some recombinations make an individual more __________, __________, and __________.
  9. Natural selection selects __________ less fit individuals.
  10. Natural selection selects __________ viable individuals. 

Elaborate

10 minutes

In this section of lesson I have students read A Bird with Many Beaksa passage from ReadWorks. the passage is at the Lexile level of 1190L. Lexile levels can be manipulated by using one of a number of online programs, such as the Google App tldr (too long didn't read) or Rewordify.

Concepts covered in in the passage:

  • Genetic variation
  • Natural selection
  • Evolution
  • Charles Darwin's finches

Students are required to answer the Text-Dependent Questions found at the end of the passage to assess comprehension. (WHST.6-8.9 - Draw evidence from informational texts to support analysis, reflection, and research.) 

As an AVID school, we use the Marking the Text reading strategy as a way for students to interact with the text.

Major Steps:

1.  Number paragraphs - an efficient way for students to refer to important ideas found in specific paragraphs.

2.  Circle Key Terms, Names of People, Names of Places, and Dates.

3.  Underline Relevant Information. 

Evaluate

5 minutes

The Exit Slip asks students to:

Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment. 

Students are required to use evidence from the modeling activity, video, and text to support their claim.

Students are required to use the CER Graphic Organizer to organize their ideas.

(MS-LS4-4. Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment/WHST.6-8.2 - Write informative/explanatory texts to examine a topic and convey ideas, concepts, and information through the selection, organization, and analysis of relevant content./SP6 Constructing Explanations and Designing Solutions)