The Process of Microevolution
Selection: Directional, Stabilizing, and
Disruptive Selection
Microevolution vs. Macroevolution
Microevolution: change in allele frequency
Macroevolution: formation of new species
Microevolution
The environment selects the best traits in the
form of alleles that are advantageous for the
given conditions
i.e. the ability to digest a new food, or a new skin
pigment may allow an organism to blend in with its
environment
Genotype = genetic make-up, what alleles an
organism has
Phenotype = appearance, what it looks like
Examples of Microevolution
Case 1: Galapagos Finch
Case 2: English Pepper Moth
Case 3: Mystery Predator
Case 4: Human Blood Types
The common denominator in each of these cases is
the change in the alleles of a given gene or set of
genes
If there is a change in the frequency of the allele(s),
then there will be a change in the genotype and
phenotype of the population
English Peppered Moth
Before industrial revolution After industrial revolution
M and M’s in the wild
The “M and M” Predator
• Showing effects of different M & M colors
surviving over time
Your turn!
Be the chocolate predator…
• Empty M and M bag on table.
• Place colors on matching dots.
• Place colors that don’t match (green)
wherever you have space.
• Now, EAT your M and M prey that don’t
match (easiest to find)
M and M PopulationBefore Predation
1st Bag Blue
1st Bag Red
1st Bag Yellow
1st Bag Green
12
Number of Individual M and M's
10
8
6
4
2
0
Type of M and M
1st Bag Orange
1st Bag Brow n
M and M PopulationAfter Predation
M and M's After Predation
Blue After
Red After
Yellow After
Green After
10
9
Number of M and M's
8
7
6
5
4
3
2
1
0
1
Color of M and M
Orange After
Brow n After
Microevolution effects on populations
over time
Life history patterns = how species reproduce
How successful each of the variations in
species will be at reproducing
Which M and M’s color will likely have a
frequency change?
Summary
The environment is the selecting force that
determines the best fit of traits.
Positive and negative selecting pressures
cause a shift in the % of a trait in a population
of a given species
The changes result in genetic shuffling
Eventually these gene shifts may be great
enough to cause species to change
Human Example
• Four Human Blood types• O is original
• A and B are two blood type changes
resulting from dietary shifts and immune
responses
• AB is newest, due to mixed A and B
populations