Lesson 18. Gene Frequency and Evolution
Estimated Time: 1 period (may take 2 if working with 45 minute periods the simulations can be lengthy)
Objective
Understand and represent the change in gene frequency in response to environmental changes through models
EQ: How can the environment affect gene expression and cause a change in gene frequency?
Bridge
Evolution will dictate a change in gene frequencies. When a variation, caused by either recombination or mutation, occurs in an organism, it may provide a survival advantage. That advantage usually results in a structural or behavioral change that will help an organism compete for resources better.
Predict some structural and behavioral changes we might see in organisms as they try to out compete those in their niche.
Mini Lesson
Changes in gene frequency (how often a gene shows up in a population) is often the result of environmental pressures. If there is a change in the environment, often organisms will start to die off or find ways to deal with that change. Some changes are small: an increase in the pH of a lake or soil by 0.01 or an increase in temperature by 1ºF. Other changes are drastic, like the impact of an asteroid that caused the extinction of the dinosaurs or the eruption of a volcano that has lain dormant for thousands of years. No matter the change, nature will respond.
Work Period
Below are different activities that deal with these environmental pressures. As you go through them, focus on how there was a shift in genes over a period of time. Represent each of these as a graph.
Stickleback Evolution: http://learn.genetics.utah.edu/content/variation/stickleback/
Rock Pocket Mice: http://learn.genetics.utah.edu/content/variation/comparative/
Paramecium Virtual Lab: http://glencoe.mcgraw-hill.com/sites/dl/free/0078759864/383928/BL_04.html
Peppered Moth Simulation: http://www.techapps.net/interactives/pepperMoths.swf
What happened to the gene frequencies of the favored genes in each of the activities?
Did the favored populations grow indefinitely? Why or why not?
Summary
Answer the EQ
Closing
Sometimes gene expression is affected directly by the environment an organism lives in. We saw a glimpse of this with the activity and skin color: people that live near the equator have an advantage if they have darker skin color and the further you get from the equator the shift is to lighter skin color.
Snowshoe hares are an example of this kind of gene expression. In the summer months, snowshoe hares are brown and in the winter months they turn white. During spring and fall, they are a combination of both colors. But these bunnies actually started out being either brown or white.
1. Explain the adaptive value of these rabbits being able to change color based on their environment.
2. Explain how the gene frequency of all three populations of rabbits changed over time (both in words and as a graph)
SPED and ELL Modifications:
1. For the work period – outline axis on the graph clearly for all four simulations
2. Allow students to work with a partner
Apps or Internet Activities:
1. Very similar to the simulations in the work period –
Darwin’s natural selection theory explained along with a flash game helping students understand how characteristics of survival are selected.
http://bio.wcupa.edu/biology/biohtml/darwin-game/darwin.swf
Independent Practice
Regents questions:
There is one on experiment with bunny and ice pack
One on change in pH of a bacteria population
The one on the lotus plants (short answer)
One on the bat population OR the rabbit population short answer where one is better adapted than the other.