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Transcript
Evolution

Catalyst
 Spider
monkeys use their claws to climb trees and reach
food. There is not enough food for everyone. A spider
monkey population has some monkeys with large claws,
and other monkeys with smaller claws.
 What is the environmental pressure exerted on this
population?
 What will happen to the frequency of the gene that
produces large claws?
 Why?
Write in complete sentences!
Don’t talk during the Catalyst!
Objectives



By the end of today…
SWBAT define species and describe how
evolution leads to new species
SWBAT analyze phylogenetic trees to
determine how related two species are
Agenda







Catalyst
Species
Where do they come from?
What happens if you cross a mouse and mango?
Phylogenetic Trees
COLLEGE LEVEL EXPLORATION! Can you handle it?
Exit Question
Microevolution
Key Point #1:
 Microevolution is the change in allele
frequency of a population over time.
 Allele frequency is the percentage that an allele
is relative to other alleles for a trait.

 Remember
that natural selection CAUSES evolution.
with good mutations survive  Reproduce  Their
offspring have that good mutation also  Allele frequency of
the good mutation increases in the gene pool
 Individuals with bad mutations die  Do not reproduce 
Allele frequency of the bad mutation decreases in the gene
 Individuals
And Why Are Populations Important?

Natural selection occurs at the
population level.
Selects
for (keeps around) helpful
mutations in a population.
Selects against (weeds out) harmful
mutations in a population.
Evolutionary Change Example




Imagine that you go to the mountaintop this year,
and sample a population of beetles.
You determine that 80% of the genes in the
population are for green coloration and 20% of
them are for brown coloration.
You go back the next year, repeat the procedure,
and find a new ratio: 60% green genes to 40%
brown genes.
What is happening???
What is happening???
Allele frequency for the green allele is
decreasing while the allele frequency
for brown allele is increasing…
This is EVOLUTION!!!
Remember allele frequency is how often an
allele occurs in a gene pool relative to other
alleles for that same gene
Another Example


Two alleles for tree frogs: green (10%) and orange (90%)
Green frogs blend in with surroundings, orange frogs don’t



What happens?



Orange frogs are eaten quickly
Green frogs live longer, have lots of offspring, pass on the gene
for being green
Allele frequency of the green allele will increase (10  70%)
Allele frequency of a orange allele will decrease. (90  30%)
What if this process happened over and over again…?


Eventually the gene pool will change - some alleles disappear
entirely (0%), some become universal (100%)!
If this is happening with many traits at the same time…BIG
CHANGES
ONE More time…
Microevolution is the
change in allele
frequency of a
population over time.
PRACTICE:


Spider monkeys have two
alleles for tails: a prehensile
tail is 30% of the population
and a short tail is 70% of the
population. A prehensile tail
helps monkeys escape from
their predators.
What will natural selection do
to the frequency of the alleles
in this population?



Butterflies can have large
wings or small wings.
80% of the butterflies have
large wings.
What percentage of the
butterflies have small
wings?
In twenty years, 40% of
the butterflies have large
wings and 60% have
small wings. WHY?
Objectives

Key Point #2
 Macroevolution
happens when changes become so big
that we get new species.

A species is a group of organisms that can produce
fertile offspring with each other.
Example of different species…

Dogs

Cats
They cannot
breed,
therefore, they
are not the
same species
Well… cool.



How do these new species originate?
I’ve enlisted this help of a few friends
for this one…
Mouse mango video
Speciation
Key Point #3
 Speciation is the process of new
species forming due to
reproductive isolation.
 Reproductive isolation means that
two organisms cannot make children.

Think Pair Share- Do you get it??
How does speciation relate
to

Mutations
Adaptations
Different
Environments?
Video: Cross a Mouse and Mango
Mouse
20
20
40
Each of these
has the correct
number of
chromosomes
The number, size, and shape of
chromosomes matter. The half
from your mom and half from
your dad have to add up to the
correct pairs. Two different
species’ chromosomes won’t pair
up right.
Mango
12
24
12
Mice and Mango
12
??
20
Phylogenetic Trees



Key Point #4: We trace
how different species
formed through
phylogenetic trees.
Organisms grow more
different as they diverge
on the tree
Common Ancestor: A
relative of two organisms
Practice


Would you expect
Feliofornia to look
more like Canifornia
or Melursus?
Would you expect
Pinnipedia to look
more like Otariidae
or Felidae?
Practice


Are diatoms more
like green algae or
gerns?
Would
archaebacteria
have more DNA in
common with Ciliates
or Slime Molds?
Practice


What process occurred
if brown algae cannot
produce fertile offspring
with red algae?
These two organisms
have a recent _____
______.
Practice


What is reproductive isolation (IN
YOUR OWN WORDS)?
How can you tell if two organisms
are part of the same species?
Exit Question


Describe what is necessary for a new species to be
made
A horse and a donkey cannot mate to produce
fertile offspring— are they in the same species?