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EVOLUTION:
PROCESSES & PATTERNS
BIOLOGY EOC BENCHMARK
SC.912.L.15.13 Describe the conditions
required for natural selection, including:
overproduction of offspring, inherited
variation, and the struggle to survive,
which result in differential reproductive
success.
VIDEO: Simpson Evolution
Why is Homer evolving?
Convergent Evolution
 different organisms that
live in similar
environments become
more alike in appearance
and behavior.
 environment selects
similar adaptations in
unrelated species.
 Organisms develop
analogous structures
(same function, but
different origins)
Coevolution
 two species evolve together.
 There is a mutual evolutionary influence
between two species.
 The species have a symbiotic relationship
(interaction between members of two
populations).
 Example: - Birds and flowers
Divergent Evolution
 ancestral species gives
rise to a number of new
species that are adapted
to different
environmental conditions
and are less alike.
 Often occurs when a
species colonizes a new
environment.
 Also known as adaptive
radiation.
THE EVOLUTIONS OF POPULATIONS
THERE ARE FOUR
MECHANISMS THAT CAN
GIVE RISE TO EVOLUTION:
1.MUTATION
2.GENETIC DRIFT
3.MIGRATION (Gene Flow)
4.NATURAL SELECTION
Greatly and quickly seen in isolated populations like those on islands.
- Allele frequency will change over generations; situations/ENV will
favor one allele over another
- Those populations at equilibrium are not evolving
- Species with more genetic diversity will adapt better to
environmental changes
GENETICS OF WHITE BENGAL TIGERS
In nature, White Bengal tigers arises from the mating of two Bengal tigers with recessive
genes for the white color of fur. The gene is recessive has the effect that offspring (cubs /
kittens) only become white if they inherit the recessive gene from both parents.
It is the same principle as with brown and blue eyes. The inbreeding producing all these
White tigers is neither good nor healthy for the tigers. In nature White tigers have, at least
theoretically as there probably arent any, a less chance of surviving than normal colored
tigers due to their lack of camouflage compared to the normal Yellow Tigers.
Below is a very simplified illustration (Fig 1) of how the transfer of genes coding for fur
color works. Consider to yellow Bengal Tigers mating. If they are both carriers of the
recessive gene there's a 25 percent chance that their cubs will be white. If a white and a
yellow Bengal tiger mates there's a 50 percent chance that the offspring will be white. The
chances of getting more White tigers can be enhanced by letting tigers that are related
mate. This is however the definition of inbreeding.
THE EVOLUTIONS OF POPULATIONS
Allele frequencies:
Proportion of orange furpigment alleles in the
population
Proportion of white furpigment alleles in the
population
Evolution is a change in the allele frequencies of a
population over time. For example, a change in the proportion
of pigment alleles in the population of tigers means that
evolution has occurred.
TIGER POPULATION
MUTATION
#1
A mutation can create
MECHANISMS
a new allele in an
OF
individual. When this
EVOLUTION
happens, the
population experiences
a change in its allele
frequencies and,
consequently,
experiences evolution.
EVOLUTIONARY CHANGE: MUTATION
Mutagen
DNA
Normal basepair sequence
Mutated basepair sequence
Normal protein
Mutated protein
Normal
phenotype
Mutated
phenotype
 Despite mutation’s vital role in
the generation of variation,
mutations almost always cause
early death or lower the
reproductive success of an
organism.
Mutations
• Are rare because you have
self correcting enzymes
• Natural Process that
produces genetic diversity
• Not all mutations are bad
– Some won’t affect the body at
all
• Blood types/ear lobes
– Some are advantageous
(thumb)
Brain Pop: Genetic Mutations
COMPUTER ACTIVITY:
Sex and the Single Guppy
The purpose of this activity is to
analyze how guppy populations
change over time. The simulation
activity allows you to start with a pool
of guppies and your choice of
predators, you will be able to watch
what happens to your guppy
population and how the introduction
of predators can affect the guppy's
appearance. The simulation will help
you understand what pressures drive
guppy evolution.
MECHANISM FOR EVOLUTION - GENETIC DRIFT
population can experience random changes in allele frequency that do not
influence reproductive success which leads to evolution
POPULATION BEFORE
GENETIC DRIFT
Allele frequencies:
cleft chin (dominant)
smooth chin (recessive)
Neither allele is
related to reproductive
success. Inheritance is
based solely on
chance.
POPULATION
AFTER GENETIC
DRIFT
There are now more
recessive alleles in the
population than
before.
REPRODUCTION
In this example, a heterozygous
couple (Cc) could have two children
that are homozygous recessive (cc),
causing an increase in the proportion
of recessive alleles in the
population.
FIXATION
Genetic drift leads to fixation when an allele’s frequency becomes
100% in a population. If this occurs, there is no longer genetic
variation for the gene.
GENETIC DRIFT - FOUNDER EFFECT
The founding members of a new population can have different allele frequencies than the
original source population and, consequently, the new population experiences evolution.
SOURCE POPULATION
Allele frequencies:
5 digits per hand
(recessive)
>5 digits per hand
(dominant)
A group of individuals may leave a
population and become the founding
members of a new, isolated population.
NEWLY FOUNDED
POPULATION
The new population will be
dominated by the genetic
features present in the founding
members.
AMISH
ARTICLE: The Amish and Founder Effect
GENETIC DRIFT - BOTTLENECK EFFECT
Occasionally, famine or disease or rapid environmental change may cause
the deaths of a large, random proportion of the individuals in a population.
SOURCE POPULATION
SOME CATASTROPHE
EXTREME AND RAPID
ENVIRONMENTAL CHANGE
NEW POPULATION
The new population will be
dominated by the genetic
features present in the
surviving members.
Unless more individuals are introduced to the
population, mating options will be limited thus
decreasing variation in the gene pool
(decreasing genetic diversity).
All cheetahs living today can trace
their ancestry back to a dozen or so
individuals that happened to survive a
population bottleneck about 10,000
years ago!
LAB: Genetic Drift Activity
#3 MECHANISMS
MIGRATION (GENE FLOW)
1 BEFORE MIGRATION
Two populations of the same species exist in
separate locations. In this example, they are
separated by a mountain range.
Population 1
OF EVOLUTION
MIGRATION
After a group of individuals
migrates from one
population to another, both
populations can experience a
change in their allele
frequencies and,
consequently, experience
evolution.
Population 2
#3
MIGRATION (GENE FLOW)
2 MIGRATION
A group of individuals from Population 1
migrates over the mountain range.
Population 1
MECHANISMS
OF EVOLUTION
MIGRATION
After a group of individuals
migrates from one population
to another, both populations
can experience a change in
their allele frequencies and,
consequently, experience
evolution.
Population 2
#3
MIGRATION (GENE FLOW)
MECHANISMS
OF EVOLUTION
MIGRATION
After a group of individuals
migrates from one population
to another, both populations
can experience a change in
their allele frequencies and,
consequently, experience
evolution.
3 AFTER MIGRATION
The migrating individuals are able to survive and
reproduce in the new population and they may
experience evolutionary changes from population 1.
Population 1
Population 2
#4
Mechanism of
Evolution
Natural Selection
1. VARIATION OF A TRAIT IN A POPULATION
3 Conditions that must
occur for Natural Selection
The tiniest dog in a litter has
reduced differential
reproductive success. Its
more robust siblings prevent
access to the food it needs to
grow and thrive.
2. The trait must be inheritable
3. One version of the trait must be in greater
abundance than a different version of the trait.
Natural Selection
There is indirect and direct evidence of
I. Indirect – we find it, not witness it
II. Direct – we are witness to the development of
Will be seen when there is:
1. Over population
2. Inheritance variation
3. Struggle for survival (abiotic factors too)
1.Fossils
2.Comparative Anatomy
3.Adaptation
Evidence:
4. Embryos
5. Biogeography
6. Field/lab Experiments
?
How long can a fruit fly
survive without food?
“SURVIVAL OF THE FITTEST”—ONLY THE ‘BEST’ FLY WILL SURVIVE
AND BE ABLE TO REPRODUCE AND PASS IT’S GENES ON TO THE NEXT
GENERATION.IT IS THEN SAID TO BE ‘FIT’-THIS IS NATURAL SELECTION.
Number of flies
AVERAGE STARVATION RESISTANCE
The average fruit fly
can survive about 20
hours without food.
A MORE
GENETICALLY
‘FIT’ FLY
GENETICALLY
‘UNFIT’” FLY
Hours until starvation
THE EXPERIMENT
= 500 fruit flies
Food removed
Food returned
Only the most starvationresistant flies live to lay eggs.
?
1 INITIAL SETUP
Start with a cage that
contains a large
number of fruit flies
(5,000), and remove
the food.
2 TESTING
STARVATION
RESISTANCE
Wait until 80% of the
starve to death,
Eggs flies
then return the food to
the cage. Record the
New generation average starvationresistance time.
Can fruit flies evolve so that they can
resist starvation longer? Can
we see Natural Selection at work? (YES)
3 START NEW
GENERATION
After the surviving flies
eat a bit, collect the eggs
those flies lay and
transfer them to a new
cage.
GENERATION 1
Average starvation resistance:
20 HR.
Hours until starvation
GENERATION 2
Average starvation resistance:
23 HR.
Hours until starvation
Experiment continues through 60 generations.
GENERATION 60
Average starvation resistance:
160 HR.---this is evolution
(change) at work
Number of flies
Number of flies
Number of flies
THE RESULTS
Hours until starvation

Over many generations of natural
selection, the population changes! The
flies now resist starvation much longer.
Natural Selection
Individuals with favorable
traits are more likely to
leave more offspring better
suited for their environment
Example:
English peppered
moth (Biston betularia)
Peppered Moth Lab
Peppered Moth Natural Selection Simulation
Peppered Moth Natural Selection Simulation
Evidence of NS: Adaption
The honeycreepers of Hawaii have adapted to a wide range of
habitats, yet still closely resemble a finch-like shared ancestor
found nearly 2,000 miles away---the major difference is the bill .
BIOGEOGRAPHY: HAWAIIAN HONEYCREEPERS
Mainland finch
(probable
shared
ancestor)
’Akeke’e
honeycreeper
BIOGEOGRAPHY:
Maui Parrotbill
honeycreeper
HONEYCREEPERS--A MODERN DAY
DARWIN’S FINCH
SCENARIO
’I’iwi
honeycreeper
Evidence of NS: biogeography
PLACENTAL COUNTERPARTS
AUSTRALIAN MARSUPIALS
BIOGEOGRAPHY: AUSTRALIAN MARSUPIALS AND THEIR PLACENTAL COUNTERPARTS
Sugar glider
Numbat
Tasmanian wolf
Gray squirrel
Giant anteater
Gray wolf

Though less related to each other than you are to a shrew,
these marsupials and their placental counterparts (both
mammals) have come to resemble each other as natural
selection has adapted them to similar habitats.
EVOLUTION BY NATURAL SELECTION: A SUMMARY
1 VARIATION
FOR A TRAIT
Different traits are present
in individuals of the same
species
2 HERITABILITY
Traits are passed on from
parents to their children.
MECHANISMS
OF EVOLUTION
NATURAL SELECTION
When these three conditions
are satisfied, the population’s
allele frequencies change and,
consequently, evolution by
natural selection occurs.
3 DIFFERENTIAL
REPRODUCTIVE SUCCESS
In a population, individuals with traits
most suited to reproduction in their
environment generally leave more
offspring than individuals with other
traits.
NATURAL SELECTION IN NATURE
Running speed in rabbits
can vary from one
individual to the next.
1 VARIATION FOR A TRAIT
The trait of running speed is
passed on from parents to
their offspring.
2 HERITABILITY
In a population, rabbits with
slower running speeds are
eaten by the fox and their
traits are not passed on to
the next generation.
3 DIFFERENTIAL
REPRODUCTIVE SUCCESS
Speed
EVOLUTION OF ANTIBIOTIC RESISTANCE
Most of the
Staphylococcus
is killed.
When first used as medicine in the 1940s, penicillin was
uniformly effective in killing the bacterium Staphylococcus
aureus. Today, natural selection has led to an increase in
antibiotic-resistant alleles, and humans are increasingly at risk
from untreatable Staphylococcus infections.(this is ongoing
evolution taking place right now )
PenicillinStaphylococcus
Kill zone
Very little of the
Staphylococcus
is killed.
1940s
Today
A single
species of
grass is
planted on a
golf course.
On the putting
greens, it is cut
very
frequently /
on the
fairways it is
cut only
occasionally /
in the rough it
is almost never
cut at all.
EVOLUTION IN PROGRESS: GREEN GRASS ON A GOLF COURSE
Over the course of
Rough
Fairway
Putting green
SELECTIVE
PRESSURE
Monthly mowing
schedule
SEXUAL
MATURATION
SLOWEST
SLOW
RAPID
SEED
PRODUCTION
LOWEST
LOW
HIGH
only a few years,
grass plants from the
same stock had
developed into three
distinct populations
as a result of the
frequency at which
they were cut.
LIFE IS SHORT
SO MUST
REPRODUCE
RAPIDLY
WITH LARGE
SEED
PRODUCTION
Evolution does not work this way
LAB: Natural Selection
(Birds on an Island)
Purpose:
• Explore how the
frequencies of
three beak
phenotypes change
over several
generations in a
population of bird
on an island.
Lab Report Format
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Title
Group Members
Benchmark
Problem
Introduction
Hypothesis
Variables
Data