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 HAPPY MONDAY 
Today you will need:
Notecards and your Journal
Please have your Notecards out and ready!
Bellwork for today:
• On the left side of your notes:
• Explain how Natural Selection works to change a
population over time?
• You must use these words: Traits, Offspring,
Adaptation, Fitness, Environment
• *Hint: Think about the bunny simulation from Friday
Journals out…
• Page:____
• Title: Mechanisms of Evolution
• EQ: What are five factors that affect
evolution?
Standard
B.7C - Analyze and evaluate how natural selection
produces change in populations, not individuals.
B.7E - Analyze and evaluate the relationship of natural
selection to adaptation and to the development of
diversity in and among species.
A quick Recap….
A gene pool is the total number of
genes of every individual in an
interbreeding population.
Evolution can be defined as a
change in the gene pool over time.
There are 5 factors that can
affect the frequency of a gene
in the gene pool.
1. Small Population
2. Non-random Mating
3. Gene Mutations
4. Gene Flow
5. Natural Selection
I. Mechanisms of Evolution
1. Small Population
a. Bottleneck effect- when
a large portion of a
population dies causing a
significant decrease in the
size of the gene pool.
b. Founder effect- when a few
individuals from a population
leave and start another
population in a different
location.
*Both examples will decrease the size of
the gene pool in the new population.
2. Non-Random Mating
1. Not all mates are created
equal.
2. In many species, mates are not
selected at random. Many
organisms compete for mating
rites. Strong and good-looking
organisms are typically favored.
3. This limits the size of the gene
pool because only the genes of
the mating individuals are
passed to the next generation.
3. Genetic Mutation
1. the source of all new genes in a gene pool and the
ultimate source of new traits in a population
4. Gene Flow: the movement of genes into or out of
a population.
a. Emigration- individuals leave a population and
decrease the size of the gene pool. “E” is for exit
b. Immigration- individuals from a different population enter a
new population and begin breeding. This increases the size of the
gene pool. “I” is for in
Genetic Drift: change in a type of genes in a
population due to a random occurrence.
• Examples of Genetic Drift
• Genetic drift refers to the change in a type of genes in a population
due to a random occurrence. In other words, a random
circumstance causes a certain genetic trait to become more
common or rarer over time.
Occurrences of Genetic Drift:
• Genetic drift can be seen in these examples:
• An exploding volcano destroys almost all of the most common trees
on a small island. Over time, the types of tree that were not affected
by the volcano continue to flourish, while the once-common tree’s
population continues to dwindle.
• Many individuals are killed due to a disease that only attacks those
with blue eyes, causing blue eyes to become rarer in the area.
5. Natural Selection
1. survival of the fittest
2. advantageous genes are passed
on to the next generation while
harmful genes are eliminated
3. the driving force of evolution
• How does the size of the gene pool affect
the rate of evolution?
Effects of Gene Pool Size
1. A decrease in gene pool size increases the
speed of evolution.
2. An increase in gene pool size reduces the speed of
evolution.
Changes in the frequency of a gene in the gene pool initially leads to
microevolution.
Microevolution refers to a small change in a population over a short
amount of time.
Many small changes eventually lead to macroevolution.
Macroevolution refers to the sum total of many changes that
transform organisms over a long period of time.
Macroevolution leads to speciation or the creation of a new species.
When an evolving population can no longer interbreed with the original
population, a new species is formed.
Changes in the frequency of a gene in a
gene pool
leads to
Microevolution: small change over a
period of time
leads to
Macroevolution: total of many changes that transform
organisms over a long period of time.
leads to
Speciation: creation of 2 different species from 1 original
species
Mix-Freeze-Group
Genetic
Mutation
Natural
Selection
Small
Population
Non-Random
Mating
• I am going to survive! Because I have the best genes for my
environment.
• I am HUGELY affected by genetic drift.
• I am VERY picky. I will only choose you, because your traits
are most attractive to me.
• I am a mistake in the DNA sequence
Scenarios
1. Amish people are required by their religion to
only marry and have children with other
Amish people.
2. The DNA sequence in a bird is changed from
ATT CCG TTG to TTA CCG TTG which changes
the beak shape from long and thin to short
and fat.
3. Peppered moths are eaten by birds. The moth
color varies from light to dark. Light colored
moths can blend in with a nearby species of
tree. In the 1800s factories released large
amounts of soot, which changed the tree color,
so the birds were able to more easily find the
lighter moths instead of the darker moths.
4. Northern elephant seals were hunted almost
to extinction by people in the 1890s. The
remaining population has reduced genetic
variation.
5. A lioness joins a new pride and has cubs with
the male lion.
6. A small group of birds flies from the mainland
to an island and starts a new colony. (The
birds never return to the mainland.)