Download Natural Selection March , 2.009 * 103

Natural Selection
November 16 , 2.009 * 103

Objective:
SWBAT

describe natural selection.
Catalyst:
What
is variation?
When
do mutations occur?
Agenda



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

Catalyst Review
Mutations… Good or Bad?
So What?
Natural Selection Notes
Natural Selection Lab
Exit Question
HW review

Questions???
Mutations Review

Mutations occur all the time. They can either INCREASE
FITNESS, DECREASE FITNESS, or NOT CHANGE FITNESS.



An example of a mutation that increases fitness:
 A cheetah got a mutation that made their legs a little longer and
they can run faster. WHY???
An example of a mutation that decreases fitness:
 A bird had a mutation that made them call at a sound frequency
that predators can hear easily. WHY???
An example of a mutation that has no effect:
 A codon that was supposed to be translated CAA gets translated
as CAG. They both still produce glutamine. WHY???
The ENVIRONMENT matters!
The
environment determines whether or
not a mutation
is good.
NOT GOOD
BECAUSE OF THE
ENVIRONMENT.
Having
extra fur might be helpful in the
north pole… but it would not be helpful in
the desert. WHY???
Putting it together…

So mutations cause variations in a population… say crickets!

Population: A group of organisms of the same species that live in
the same environment

There are just all these different crickets hanging out until…

Key Point #1:

When a significant environmental pressure arises, certain traits
will be “selected” for.
Environmental Pressures

Examples:
 In
a population of lions, a shortage of prey can cause
certain types of lions to be selected for…
 What
is the environmental pressure?
 What kind of lions would be selected for?
 In
a population of peacocks, a shortage of mates can
cause certain types of peacocks to be selected for…
 What
is the environmental pressure?
 What kind of peacocks would be selected for?
So what?


What happens to mutations that
decrease fitness?
What happens to mutations that
increase fitness?
Natural Selection


Key Point #2:
 Natural selection is the process by which
mutations that increase fitness become more
common over time, and mutations that decrease
fitness become less common over time.
“Common” where?
 The
gene pool is all the genes in a population of an
organism.
Natural Selection

Good mutations are “selected for” (kept around) by natural
selection
 A good mutation gives an organism an advantage that
lets it produce more offspring.
 Many organisms will be born with the mutation, and it will
become more common in the gene pool.
REALLY IMPORTANT!!!
Make sure to get this down
IN YOUR OWN WORDS!!!
Natural Selection

Bad mutations are “selected against” (weeded out) by
natural selection
 A bad mutation gives an organism a disadvantage that
causes it to produce fewer offspring.
 Few organisms will be born with the mutation, and it will
become less common in the gene pool.
REALLY IMPORTANT!!!
Make sure to get this down
IN YOUR OWN WORDS!!!
Environmental effect

AWESOME EVOLUTION DEMO
Guided Practice 1

Koalas have hands and feet that allow them to have
a vice grip on tree branches.
 What
caused this trait?
 Is this beneficial to the koala? Why?
 What about the environment makes it beneficial?
 What will happen to this trait in the gene pool?
 In what environment would this trait not be helpful?
Guided Practice 2

Wolves developed thick fur in the desert.
 What
caused this trait?
 Is this beneficial to the wolf? Why?
 What about this environment makes it harmful?
 What will happen to this trait in the gene pool?
 In what environment would this trait be helpful?
Let’s Model Natural Selection


To model how natural selection occurs, we will do a
QUACKERS lab!
Remember: It is the ENVIRONMENT that determines
if a mutation is good!!!
Exit Questions

What determines if an mutation is good or bad?

Describe natural selection.

Tricky! Give an example of a good mutation of any
animal. Look back at this tomorrow and see if it still
holds true.