Download Agents of Evolutionary Change

Agents of Evolutionary
Change
Or Disruption of Genetic Equilibrium
Last Class
Chapter 15 Review
Fossils
Evolutionary Theorists
Evolutionary Evidence
Processes of Evolution
Build-A-Beast Workshop (Due Monday Oct 5, along
with presentation)
Test – Evolution- Wednesday Oct 7
Today
We will discuss how Evolution occurs in
populations
Agents of Evolutionary change
AKA Disruption of Genetic Equilibrium
Genetic Drift Activity
Computer Lab time
But First… Evolution Quiz!
Everything off your tables except for a
writing utensil!
5 min (shouldn’t take too much longer…)
Back to the Lesson…
But First…
Let’s do a Think- Pair- Share
What traits would a NON-EVOLVING
population have?
What factors would keep this
population from evolving?
Hardy-Weinberg Genetic Equilibrium
Of course we know by now, that populations do
evolve… but typically not at any rate which we
can really see.
populations tend to remain the same from
generation to generation, unless enacted on by
an outside influence
This is what is known as the Hardy-Weinberg
Genetic Equilibrium (HWE)
Hardy-Weinberg Genetic Equilibrium
It is based on a set of assumptions about a
hypothetical and ideal population that is not
evolving;
1. No Net Mutations occur
2. Individuals do not enter or leave the
population
3. The population is large (ideally, infinitely)
4. Individuals mate randomly
5. Selection does not occur
HWE Continued
Of course, there is no population like
that…
The HWE is used to measure the rate
of evolutionary change in a
population, by comparing it to an
ideal, never evolving population
Let’s Look Back at the “Ideal” NonEvolving Population…
1. No Net Mutations occur
2. Individuals do not enter or leave the
population
3. The population is large (ideally, infinitely)
4. Individuals mate randomly
5. Selection does not occur
An Evolutionary change in a population would
therefore involve one of these changes to occur.
Agents of Evolutionary change
Mutation, Genetic Drift, Migration
(Gene Flow), Non-Random Mating,
Natural Selection
Mutations
We have learned how mutations are copying
errors during DNA replication. Mutations can
happen in different ways:
Substitutions
ACTGCGA  ACTGCCT
(sickle cell anemia)
Insertion
ACTGCGA  ACTGACGA
Deletions
ACTGCGA  ACTCGA
G
Insertions and Deletions lead to Frameshifts
Mutations (cont’d)
Types of mutations:
Neutral
Most common. Change in DNA sequence
that has no affect on protein synthesis
Harmful
Second most common: change in DNA
sequence leads to harmful trait
Beneficial
Least common, mutation leads to trait
which serves beneficial to organism. Driving
force of evolution
Genetic Drift
The Hardy-Weinberg equilibrium does not hold for
small or medium populations
Genetic drift is the phenomenon by which allele
(genetic traits) frequencies in a population change
as a result of RANDOM events or CHANCE
In a small population the FAILURE or GREATER THAN
NORMAL RATE of one organism to reproduce can
significantly disrupt gene frequency
Loss in genetic variation means there is nothing for natural
selection to act upon
- Positive or Negative traits can’t be selected if all genes
across population are similar
Genetic Drift- Bottleneck effect
Genetic Drift- Founders Effect
Now let’s see genetic drift in action…
 In groups of 3, grab one cup of candy, and one worksheet
 Follow directions, and complete questions
 When finished
In your Notebook
Explain in your own words the positives and negatives of
mutations on an INDIVIDUAL.
Why might mutations be more beneficial on a POPULATION?
Why are species in danger of extinction if there is no variation in
allele (gene) frequencies in the population?
Next Class
Look at the other 3 agents of Evolutionary
change
Migration (Gene Flow)
Non-random mating
Natural Selection