Download Mechanisms of Evolution

Mechanisms of Evolution
SWABT’s
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Students will be able to explain how mutations are important in how populations
change over time.
Students will be able to illustrate why adaptations sometimes arise in response to
environmental pressures.
Students will be able to consider how many factors can cause a change in a gene
over time.
Students will be able to compare the rate of adaptation, the rate of reproduction,
and the environmental factors present, to infer how structural adaptations may
take millions of years to develop.
Engage
Students will see an overhead of two rivers on two isolated islands. One river is
clear, while the other one is dark and cloudy. The students will have to answer these two
questions:
1. Stream A and Stream B are located on two isolated islands with similar characteristics.
How do these two stream beds differ?
2. Suppose a fish that varies in color from a lighter shade to a darker shad is introduced
from Stream A to Stream B, How might the color of the fish population in Stream B
change over time?
Explore
Students will do a lab that uses M & M’s to show the allelic frequencies of a tiger
population. There are multiple questions to follow that help explain terms such as
genetic equilibrium, allelic frequency, speciation, and other population genetics concepts.
Explain
Students will come back together to discuss what they found in the lab. What
types results were found? Were the results from group to group similar or different?
After this the teacher will discuss other concepts such as genetic drift, stabilizing
selection, directional selection, reproductive isolation, and speciation. Students can ask
questions and the teacher can provide examples, using what they have learned in previous
lessons as well as in the lab completed in the ‘Explore’ portion of class.
Expand
Students will look at pictures of unrelated species of plants that live in the same
area. They will note their differences and similarities. Students will be asked, how
unrelated plants look very similar. After some questioning students should see that it was
the environment that caused similar structures to be chosen in natural selection. This is a
type of convergent evolution. Because the plants share similar environmental pressures,
they share similar pressures for natural selection.
Evaluate
Students will be asked one question. What evolves, a population or an
individual? They can answer this on a note card.