Evolution
Unit
 Chapters 22, 23,
24, 25 and 26
AP Biology
What is Evolution?
• Change in the genetic makeup of a population
over time.
• Fitness – those with favorable variations for
survival and reproduction.
– Populations can evolve, not individuals.
• Diverse gene pool good for long-term survival
of a species. Genetic variations are important!
• How do genetic variations occur?
Where does Variation come from?
 Mutation

random changes to DNA
 errors in mitosis & meiosis
 environmental damage
 Sexual reproduction

mixing of alleles
 genetic recombination
 new arrangements of alleles in every offspring
 new combinations = new phenotypes
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Genetic variation in a population
Essence of Darwin’s ideas
 Natural selection
heritable variation exists in populations
 over-production of offspring

 more offspring than the environment can support

competition
 for food, mates, nesting sites, escape predators

differential survival
 successful traits = adaptations

differential reproduction
 adaptations become more
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common in population
Lamarckian vs. Darwinian view
 LaMarck

in reaching higher
vegetation giraffes
stretch their necks &
transmits the acquired
longer neck to offspring

 Darwin

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giraffes born with longer
necks survive better &
leave more offspring who
inherit their long necks
Natural Selection
•
•
•
•
Major mechanism of evolution
Environment is always changing
Acts upon the phenotype of the population
Based on Darwin’s idea that resources are limited
and that there is competition for those resources.
• Adaptation = a genetic variation favored by
natural selection.
• When allele frequencies shift, speciation occurs
– Thus, the frequency change is NOT RANDOM
Effects of Selection
 Changes in the average trait of a population
DIRECTIONAL
SELECTION
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giraffe neck
horse size
STABILIZING
SELECTION
DISRUPTIVE
SELECTION
human birth weight
rock pocket mice
Natural selection
in action
Resistance…
NOT immunity!
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MRSA
Heterozygote Advantage
 Keeps the recessive
allele in the population
 Ex: Sickle Cell Anemia



aa – dies of sickle cell
anemia
Aa – some side affects
BUT resistant to malaria!
AA – no disease present
BUT prone to malaria
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Hidden variations can be exposed through selection!
Terminal
bud
Lateral
buds
Cabbage
Artificial selection
Brussels
sprouts
Leaves
Flower cluster
Kale
Cauliflower
Stem
Flower
and
stems
Broccoli
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Wild mustard
Kohlrabi
In addition to natural
selection, evolutionary
change is also driven
by random processes…
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Genetic Drift
 Chance events changing frequency of
traits in a population

not adaptation to environmental conditions
 not selection

founder effect
 small group splinters off & starts a new colony
 it’s random who joins the group

bottleneck
 a disaster reduces population to
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small number & then population
recovers & expands again but
from a limited gene pool
 who survives disaster may be random
Ex: Cheetahs
 All cheetahs share a small number of alleles

less than 1% diversity
 2 bottlenecks

10,000 years ago
 Ice Age

last 100 years
 poaching & loss of habitat
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Conservation issues
 Bottlenecking is an important
Peregrine Falcon
concept in conservation
biology of endangered
species
loss of alleles from gene pool
 reduces variation
 reduces adaptability

Breeding programs must
consciously
outcross
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Golden Lion
Tamarin
Human Impact on variation
 How do we affect variation in other
populations?

Artificial selection/Inbreeding
 Animal breeds

Loss of genetic diversity
 Insecticide usage

Overuse of antibiotics
 resistant bacterial strains
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Hardy Weinberg: Population Genetics
Using mathematical approaches
to calculate changes in allele
frequencies…this is evidence of
evolution.
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Hardy-Weinberg equilibrium
 Hypothetical, non-evolving population

preserves allele frequencies
 natural populations rarely in H-W
equilibrium

useful model to measure if forces are acting on
a population
 measuring evolutionary change
G.H. Hardy
AP mathematician
Biology
W. Weinberg
physician
Evolution of populations
 Evolution = change in allele frequencies
in a population

hypothetical: what conditions would
cause allele frequencies to not change?
1. very large population size (no genetic drift)
2. no migration (no gene flow in or out)
3. no mutation (no genetic change)
4. random mating (no sexual selection)
5. no natural selection (everyone is equally fit)
H-W occurs ONLY in non-evolving
populations!
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Populations & gene pools
 Concepts
a population is a localized group of
interbreeding individuals
 gene pool is collection of alleles in the
population

 remember difference between alleles & genes!

allele frequency is how common is that
allele in the population
 how many A vs. a in whole population
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H-W formulas
 Alleles:
p+q=1
B
 Individuals:
p2 + 2pq + q2 = 1
BB
BB
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b
Bb
Bb
bb
bb
Origin of the Equation
 Assuming that a trait is
recessive or dominant

Allele pairs AA, Aa, aa
would exist in a population
 p+q=1
 The probability that an
individual would
contribute an A is called p
 The probability that an
individual would
contribute an a is called q
 Because only A and a are
present in the population
the probability that an
individual would donate
one or the other is 100%
 p2 + 2pq + q2
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Male
Gametes
A(p)
Male
Gametes
a(q)
Female
gametes
A(p)
AA
p2
Aa
pq
Female
Gametes
a(q)
Aa
pq
aa
q2
Hardy-Weinberg theorem
 Counting Alleles
Frequencies are
usually written as
decimals!
assume 2 alleles = B, b
 frequency of dominant allele (B) = p
 frequency of recessive allele (b) = q

 frequencies must add to 1 (100%), so:
p+q=1
BB
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Bb
bb
Hardy-Weinberg theorem
 Counting Individuals



frequency of homozygous dominant: p x p = p2
frequency of homozygous recessive: q x q = q2
frequency of heterozygotes: (p x q) + (q x p) = 2pq
 frequencies of all individuals must add to 1 (100%), so:
p2 + 2pq + q2 = 1
BB
AP Biology
Bb
bb
Practice Problem:
 In a population of 100 cats, there are 16

white ones. White fur is recessive to
black.
What are the frequencies of the
genotypes?
AP Biology
Use Hardy-Weinberg equation!
q2 (bb): 16/100 = .16
q (b): √.16 = 0.4
p (B): 1 - 0.4 = 0.6
p2=.36
BB
2pq=.48
Bb
q2=.16
bb
MustWhat
assume
are population
the genotype
is in
frequencies?
H-W equilibrium!
AP Biology
Answers:
p2=.36
Assuming
H-W equilibrium:
Expected data
Observed data
How do you
explain
the data?
AP
Biology
2pq=.48
q2=.16
BB
Bb
bb
p2=.20
=.74
BB
2pq=.64
2pq=.10
Bb
q2=.16
bb
Tips for Solving HW Problems:
 Solve for q first.
 Then solve for p.
 Don’t assume you can just solve for p2

if only given dominant phenotypic
frequency.
READ carefully!!! HW Math is fun 
AP Biology
Example of an evolving population:
 Peppered moth



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Variation of colors in the population existed (Black,
Peppered, White)
As environmental conditions changed, the frequency of
the recessive allele increased.
This was seen as an adaptation to the environment that
allowed the species to survive and reproduce better.
2006 Fossil Discovery of Early Tetrapod
“Tiktaalik”
“missing link” from sea to land animals
Evidence Supporting Evolution
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Evidence for Evolution
• Paleontology – fossils show change in a species
•
•
over time
Biogeography – Similar species are found in
similar ecosystems around the world
Morphology – Comparing structures
–
–
Homologous structures – body parts with
similar structure but possible different function.
Shows common ancestry
Analogous structures – similar structure
develops in organisms that share a common
ecosystem but not a common ancestry
• Biochemical or Molecular AP Biology
–
Similarities in gene sequences, proteins, DNA
Fossils
 Preserved remains of living things
 Paleontology is the study of the fossil

record
Most organisms do not leave a fossil after
death

Explains the “missing links”
 Sedimentation Fossils

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As the organism decomposes the
spaces will be filled with the minerals
from the silt
The Archaeopteryx Fossil
Reptilian Features
Forelimb has three
functional fingers
with grasping
claws.
Lacks the
reductions and
fusions present in
other birds.
Breastbone is small
and lacks a keel.
True teeth set in
sockets in the jaws.
The hind-limb girdle
is typical of
dinosaurs, although
modified.
Long, bony tail.
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Avian Features
Vertebrae are
almost flatfaced.
Impressions of
feathers attached
to the forelimb.
Belly ribs.
Incomplete fusion
of the lower leg
bones.
Impressions of
feathers attached
to the tail.
LEFT: Archaeopteryx lithographica
Found in 1877 near Blumenberg, Germany
How old is that fossil?
 Relative Dating

Age of fossils based according to their location
in strata
 Absolute Dating

Age of fossils determined by analyzing the
content of radioactive isotopes found in the
fossil.
Half-life: The length of time required for half of the
radioactive elements to change into another stable
element.
Unaffected by temperature, light, pressure, etc.
All radioactive isotopes have a dependable half life.
Ex: C14 decays into N14
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Relative Dating
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Absolute Dating
How radioactive
“naturally
occurring”
elements get inside
an organism:
A.K.A –
Radiometric dating
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Homologous Structures
Anatomical evidence
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Analogous structures
Convergent
Don’t
be fooled
by evolution
their looks!
Those
tails
Does fins
this &
mean
& sleek
they bodies
have a are
recent
common
ancestor?
analogous
structures!
Solving a similar problem with a similar solution
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Molecular Homology
Human
Macaque
Dog Bird
Frog
Lamprey
The sequence in
DNA
proteins
Why &compare
is a &molecular
DNA
proteins
record
of evolutionary
across
species?
relationships.
Comparative hemoglobin structure
8
0
32
45
67
125
10 20 30 40 50 60 70 80 90 100 110 120
Number of amino acid differences between
hemoglobin (146 aa) of vertebrate species and that of humans
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Vestigial organs
Why would whales
have pelvis & leg bones
if they were always
sea creatures?
AP Biology
These are
remnants of
structures that were
functional in
ancestral species
Evolution evidence at the cellular level
 Domains: Archaea, Bacteria and
Eukarya

Elements conserved through all: DNA,
RNA and many metabolic pathways.
 Eukaryotes – core features:
Cytoskeleton
 Nucleus
 Membrane-bound organelles
 Linear chromosomes
 Endomembrane system

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The Origin of Species
Mom, Dad…
There’s something
you need to know…
I’m a MAMMAL!
AP Biology
2010-2011
Speciation
• Changes in allele frequency are so great
that a new species is formed
• Can be slow and gradual or in “bursts”
• Extinction rates can be rapid and then
adaptive radiation follows when new
habitats are available
Correlation of speciation to food sources
Seed
eaters
Flower
eaters
Insect
eaters
Rapid speciation:
new species filling niches,
because they inherited
successful adaptations.
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Adaptive
So…what is a species?
• Population whose members can
interbreed & produce viable, fertile
offspring
• Reproductively compatible
Distinct species:
songs & behaviors are different
enough to prevent interbreeding
Eastern Meadowlark Western Meadowlark
How do new species originate?
 When two populations become
reproductively isolated from each other.
 Speciation Modes:

allopatric
 geographic separation
 “other country”

sympatric
 still live in same area
 “same country”
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Allopatric Speciation
 Physical/geographical
separation of two populations
 Allele frequencies diverge
 After a length of time the two
population are so different
that they are considered
different species
 If the barrier is removed
interbreeding will still not
occur due to pre/post zygotic
isolation
Sympatric Speciation
Formation of a new species without geographic isolation.
Causes:
– Pre-zygotic barriers exist to mating
– Polyploidy (only organism with an even number of
chromosomes are fertile…speciation occurs quickly)
– Hybridization: two different forms of a species mate
in common ground (hybrid zone) and produce
offspring with greater genetic diversity than the
parents….eventually the hybrid diverges from both
sets of parents
Pre-zygotic Isolation
Sperm never gets a chance to meet egg
•Geographic isolation: barriers prevent mating
•Ecological isolation: different habitats in same
region
•Temporal isolation: different populations are
fertile at different times
•Behavior Isolation: they don’t recognize each
other or the mating rituals
•Mechanical isolation: morphological differences
•Gamete Isolation: Sperm and egg do not
recognize each other
PRE-Zygotic barriers
 Obstacle to mating or to fertilization if
mating occurs
geographic isolation
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behavioral isolation
ecological isolation
temporal isolation
mechanical isolation
gametic isolation
Post Zygotic Isolation
• Hybrid Inviability – the
embryo cannot develop
inside the mothers womb
• Hybrid Sterility – Adult
individuals can be
produced BUT they are
not fertile
• Hybrid Breakdown – each
successive generation has
less fertility than the
parental generation
Evolutionary Time Scale
• Microevolution – changing
of allele frequencies in a
population over time.
• Macroevolution – patterns
of change over geologic
time. Determines
phylogeny
– Gradualism – species are
always slowly evolving
– Punctuated equilibrium –
periods of massive
evolution followed by
periods with little to no
evolution
Patterns of Evolution
• Divergent Evolution (adaptive radiation)
• Convergent Evolution
–
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Two or more species that share a
common environment but not a common
ancestor evolve to be similar
Is it a shark or a
dolphin??
Coevolution
 Two or more species reciprocally
affect each other’s evolution

predator-prey
 disease & host
competitive species
 mutualism

 pollinators & flowers
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Mass Extinctions
• At least 5 mass extinctions have occurred throughout
history.
• Possible causes: dramatic climate changes occurring
after meteorite collisions and/or continents drift into new
and different configurations.
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Origin of the Earth
What must Earth have been like
before living things took over?
AP Biology
The Primitive Earth
 Atmosphere:
All chemicals/compounds necessary are thought
to have originated on earth
 Inorganic precursors:
 Water vapor
 Nitrogen
 Carbon dioxide
 Small amounts of hydrogen and carbon
monoxide
 These were the monomers for forming more
complex molecules.
 Experiments have shown that it is possible to form
organic from inorganic.

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Electrodes discharge
sparks
(lightning simulation)
Origin of Organic Molecules
 Abiotic synthesis
1920 - Oparin
first molecules
formed by strong
energy sources
 1953 - Miller & Urey
test hypothesis

Water vapor
CH4
NH3
Mixture of gases
("primitive
atmosphere")
H2
Condenser
Water
 formed organic
compounds
 amino acids
 adenine
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Heated water
("ocean")
Condensed
liquid with
complex,
organic
molecules
Key Events in Origin of Life
 Origin of Cells (Protobionts)

lipid bubbles  separate inside from outside
 metabolism & reproduction
 Origin of Genetics


RNA is likely first genetic material
multiple functions: encodes information (selfreplicating), enzyme, regulatory molecule,
transport molecule (tRNA, mRNA)
 makes inheritance possible
 makes natural selection & evolution possible
 Origin of Eukaryotes

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endosymbiosis
Timeline
 Key events in
evolutionary
history of life on
Earth
3.5–4.0 bya:
life originated
 2.7 bya:
free O2 =
photosynthetic
bacteria
 2 bya:
first eukaryotes

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~2 bya
First Eukaryotes
 Development of internal membranes


create internal micro-environments
advantage: specialization = increase efficiency
 natural selection!
infolding of the
plasma membrane
plasma
membrane
endoplasmic
reticulum (ER)
nuclear envelope
nucleus
DNA
cell wall
Prokaryotic
cell
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Prokaryotic
ancestor of
eukaryotic
cells
plasma
membrane
Eukaryotic
cell
1st Endosymbiosis
 Evolution of eukaryotes



origin of mitochondria
engulfed aerobic bacteria, but
did not digest them
mutually beneficial relationship
 natural selection!
internal membrane
system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
AP
Biology
eukaryotic
cell
Eukaryotic cell
with mitochondrion
2nd Endosymbiosis
 Evolution of eukaryotes



Eukaryotic
cell with
mitochondrion
origin of chloroplasts
engulfed photosynthetic bacteria,
but did not digest them
mutually beneficial relationship
 natural selection!
photosynthetic
bacterium
chloroplast
Endosymbiosis
Eukaryotic cell with
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chloroplast & mitochondrion
mitochondrion
Theory of Endosymbiosis
 Evidence

structural
 mitochondria & chloroplasts
resemble bacterial structure

genetic
Lynn Margulis
 mitochondria & chloroplasts
have their own circular DNA, like bacteria

functional
 mitochondria & chloroplasts
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move freely within the cell
 mitochondria & chloroplasts
reproduce independently
from the cell
Cambrian explosion
 Diversification of Animals

543 mya
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within 10–20 million years most of the major
phyla of animals appear in fossil record