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Trial 3 - Mutations

[model: mutation]

1. The change in teeth demonstrates how an existing trait could become more or less common in a population, in response to selection pressure from the environment. But it doesn't explore how new features could arise that weren't present at all. New features arise from mutations in the genes -- chance alterations in genetic structure that change the organism.

2. Suppose a mutation occurs in an individual animal. What do you think would happen if the mutation had these different effects on the animal?

   Effect of mutation	Mutation will:			Why?
   	Become common	disappear	Remain at a low level
   Has a greater number of offspring
   More resistant to some deadly disease
   Less attractive to potential mates
   No change in the animal

   
   

3. Now explore these questions in the model. In this version, all of the sheep have standard teeth. There is a new feature -- an ADD MUTANTS button. When you hit this button, some blue sheep are added to the herd. Sheep pass their color gene on to their offspring.

4. If SELECTION? = ON, a blue sheep gets twice as much energy from grass as a regular sheep. If SELECTION? = OFF, the blue color has no effect on its eating or how likely it is to survive and have offspring.

5. Open the model. Set SELECTION? = OFF. Run the model and let the population settle down. Hit the ADD MUTANT button. Watch the BLUE SHEEP monitor. What happens to the number of blue sheep?
   
   
6. Keep running the model and add more blue sheep. Does the mutation become common?
   
   
7. What can you conclude about a mutation that is neither favorable nor unfavorable?
   
   

8. Now set SELECTION? = ON. This changes the model so that blue sheep also have much better teeth. This linkage between color and teeth is completely arbitrary! It was done so that you could see whether the mutation becomes more common as time goes by.

9. Run the model and add a mutation. If the mutation dies out, add a few more. What happens?
   
   
10. How does selection help a mutation to become more common?
    
    
11. What if the mutation were not favorable? Would it become more common?
    
    
12. Here's a variation on the model. Suppose that blue sheep had much better teeth, but females refused to mate with blue males. What do you think would happen?
    
    
13. Open the 'fussy females' model. [sheep-fussyfemales model] Try the model with SELECTION? on or off, and FUSSYFEMALES? on or off. Run the model, add at least 15 mutants, and fill in the following table.

    Condition	What happens
    SELECTION? = OFF FUSSYFEMALES? = ON
    SELECTION? = ON FUSSYFEMALES? = OFF
    SELECTION? = ON FUSSYFEMALES? = ON