Download Mechanisms of Evolution

 HAPPY MONDAY 
Today you will need: Notecards and your Journal
Please have your Notecards or Late Video Homework out and ready to be
checked!
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.
I. Mechanisms of Evolution
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
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 goodlooking 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.
b. Immigration- individuals from a different population enter a new population and
begin breeding. This increases the size of the gene pool.
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
Gene pools can change in 3 different
ways:
a. Disruptive selection
b. Directional selection
c. Stabilizing selection
1. Disruptive selection: individuals on the
upper and lower ends of a distribution
curve are more fit than organisms in the
middle, curve becomes a U-shaped.
2. Directional selection: when organisms at
one end of the distribution curve have the
highest fitness, shifts the curve in one
direction.
3. Stabilizing selection: when individuals in
the middle of the distribution curve have
the highest fitness, the curve does not
move/change.
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