EVOLUTION/POPULATION GENETICS

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EVOLUTION/POPULATION GENETICS

• CH. 15-16

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SOME INFLUENCES ON DARWINS THOUGHT

• LAMARCK
• MALTHUS
• LYELL
• HUTTON
• WALLACE

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Contributors to Darwins thinking included

• Charles Lyell uniformatarianism
• Georges Cuvier species extinction
  (Catastrophism)
• Thomas Malthus struggle for existence
  (resources)

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Contributors to Darwins thinking included

• James Hutton - Gradualism
• John Baptiste Lamarck Inheritance of acquired
  Characteristics and Law of Use and Disuse
• Alfred Russel Wallace organisms evolved from
  common ancestors

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Lamarcks Theory of Evolution

• Jean-Baptiste Lamarck, 1809
• One Of First Scientists To Understand That Change
  Occurs Over Time
• Stated that Changes Are Adaptations To
  Environment acquired in an organisms lifetime
• Said acquired changes were passed to offspring

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Lamarcks Theory of Evolution

• Idea called Law of Use and Disuse
• If a body part were used, it got stronger
• If body part NOT used, it deteriorated

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Lamarcks Theory of Evolution

• Inheritance Of Acquired Traits
• Traits Acquired During Ones Lifetime Would Be
  Passed To Offspring

Clipped ears of dogs could be passed to offspring!
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Lamarcks Mistakes

• Lamarck Did NOT Know how traits were inherited
  (Traits are passed through genes)
• Genes Are NOT Changed By Activities In Life
• Change Through Mutation Occurs Before An Organism
  Is Born

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Population Growth

• Thomas Malthus, 1798
• Economist
• Observed Babies Being Born Faster Than People
  Were Dying
• Population size limited by resources such as the
  Food Supply

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The Struggle for Existence

• Malthus Influence
• High Birth Rates Limited Resources Would Force
  Life Death Competition
• Each Species Struggles For
• Food
• Living Space
• Mates

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Population Growth

• Malthus Reasoned That If The Human Population
  Continued To Grow Unchecked, Sooner or Later
  There Would Be Insufficient Living Space Food
  For Everyone
• Death Rate Will Increase To Balance Population
  size Food Supply

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Population Growth

• Darwin Realized Malthuss Principles Were Visible
  In Nature
• Plants Animals Produce Far More Offspring Than
  Can Be Supported
• Most Die
• If They Didnt Earth Would Be Overrun

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Charles Lyell

• Proposed theory of Uniformitarianism
• Geological processes at uniform rates building
  wearing down Earths crust
• Proposed that the Earth was millions of years
  instead of a few thousand years old

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Principles of Geology

• Published by Lyell Just Before The Beagle Set
  Sail read by Darwin
• Explained Geological Processes That Shaped The
  Earth
• Helped Darwin Understand Sea Shells In The Andes
  Mountains At 12,000 Feet
• Expanded Earths Age

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Huttons Theory of Geological Change

• James Hutton, 1795, Scottish geologist
• Studied invertebrate fossils in Paris Museum
• Described The Geological Forces That Have Changed
  Life on Earth Over Millions of Years (erosion,
  earthquakes, volcanoes)

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Huttons Theory of Geological Change

• Changes in Earths crust due to slow continuous
  processes
• Idea Known as Gradualism

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Wallaces Contribution

• Alfred Russel Wallace Independently came to same
  Conclusion as Darwin that species changed over
  time because of their struggle for existence
• When Darwin read Wallaces essay, he knew he had
  to publish his findings

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Darwin's Theory

1. Individual Organisms In Nature Differ From One
   Another. Some Of This Variation Is Inherited
2. Organisms In Nature Produce More Offspring Than
   Can Survive, And Many Of These Offspring Do No
   Reproduce

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Darwin's Theory

1. Because More Organisms Are Produced Than Can
   Survive, Members Of Each Species Must Compete For
   Limited Resources
2. Because Each Organism Is Unique, Each Has
   Different Advantages Disadvantages In The
   Struggle For Existence

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Darwin's Theory

1. Individuals Best Suited To Their Environment
   Survive Reproduce Successfully Passing Their
   Traits To Their Offspring.
2. Species Change Over Time. Over Long Periods,
   Natural Selection Causes Changes That May
   Eventually Lead To New Species

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Darwin's Theory

1. Species Alive Today Have Descended With
   Modifications From Species That Lived In The Past
2. All Organisms On Earth Are United Into A Single
   Tree Of Life By Common Descent

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Concept Map
Section 15-3
Evidence of Evolution
includes
which is composed of
which indicates
which implies
which implies
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Homologous Structures
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HOMOLOGOUS STRUCTURES
Section 15-3
Turtle
Alligator
Bird
Mammal
Ancient lobe-finned fish
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Homologous Body Structures

• Not All Serve Important Functions
• Vestigial Organs
• Appendix In Man
• Legs On Skinks

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Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
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Fossil Record

• Earth is Billions of Years Old
• Fossils In Different Layers of Rock (sedimentary
  Rock Strata) Showed Evidence Of Gradual Change
  Over Time

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Geographic Distribution of Living Species
Section 15-3
Beaver
Beaver Muskrat Beaver andMuskrat Coypu
Capybara Coypu andCapybara
NORTH AMERICA
Muskrat
Capybara
SOUTH AMERICA
Coypu
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Similarities in DNA Sequence
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Evolutionary Time Scales
Macroevolution Long time scale events that
create and destroy species.
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Evolutionary Time Scales
Microevolution Short time scale events
(generation-to-generation) that change the
genotypes and phenotypes of populations
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VARIATION GENE POOLS GENE POOL, RELATIVE
FREQUENCY OF GENES/ALLELES
Section 16-1
Sample Population
Frequency of Alleles
allele for brown fur
allele for black fur
48 heterozygous black
16 homozygous black
36 homozygous brown
Relative frequency? of times an allele occurs
in a gene pool, compared w/ the of times other
alleles for the same gene occur
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MUTATION

• THE ULTIMATE SOURCE OF GENETIC VARIATION!!!!!!

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 Phenotypes for Single-Gene Trait The of
phenotypes a given trait has is determined by how
many genes control the trait
Section 16-1
100 80 60 40 20 0
Controlled by a single gene that has 2 alleles?
leads to 2 distinct phenotypes
Frequency of Phenotype ()
Widows peak
No widows peak
Phenotype
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Generic Bell Curve for Polygenic Trait many
possible genotypes and phenotypes
Section 16-1
Controlled by 2/ more genes (2/ more alleles
Frequency of Phenotype
Phenotype (height)
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NATURAL SELECTION ON POLYGENIC TRAITS 3 MODELS
Section 16-2
Key
Directional Selection
Low mortality, high fitness
High mortality, low fitness
Food becomes scarce.
Favors traits at 1 extreme of a range of traits
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Graph of Stabilizing Selection
Section 16-2
Stabilizing Selection
Individuals with the most common trait are most
adapted, while individuals who differ from the
norm are poorly adapted.
Key
Low mortality, high fitness
Selection against both extremes keep curve narrow
and in same place.
High mortality, low fitness
Percentage of Population
Birth Weight
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Graph of Disruptive Selection
Section 16-2
Disruptive Selection
Largest and smallest seeds become more common.
Key
Population splits into two subgroups specializing
in different seeds.
Low mortality, high fitness
Number of Birdsin Population
Number of Birdsin Population
High mortality, low fitness
Beak Size
Beak Size
When both extreme phenotypes are favored by
natural selection
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Balancing Selection
Natural selection acts in opposite
directions Heterozygote Advantage- ind who
is heterozygous for a particular gene has a
greater fitness than a homozygous ind EX
Distribution of sickle-cell allele coincides with
the occurrence of malaria SS Normal
hemoglobin ss Sicke-cell disease
Ss- codominance (protects against malaria)
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GENTIC DRIFT A RANDOM CHANGE IN ALLELE FREQUENCY

• IN SMALL POPULATIONS, INDIVIDUALS THAT CARRY A
  PARTICULAR ALLELE MAY LEAVE MORE DESCENDANTS THAN
  OTHER INDIVIDUALS, JUST BY CHANCE. OVER TIME, A
  SERIES OF CHANCE OCCURRENCES OF THIS TYPE CAN
  CAUSE AN ALLELE TO BECOME COMMON IN A POPULATION.
• FOUNDER EFFECT A SITUATION IN WHICH ALLELE
  FREQUENCIES CHANGE AS A RESULT OF THE MIGRATION
  OF A SMALL SUBGROUP OF A POPULATION.

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Genetic Drift
Section 16-2
Sample of Original Population
In small populations, an allele can become more
or less common by chance (explain how allele
frequencies can fluctuate unpredictably from 1
gen to the next)
Descendants
Founding Population A
Founding Population B
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Genetic Drift
Section 16-2
Sample of Original Population
Descendants
FOUNDER EFFECT 2 small groups from a large,
diverse population could produce new populations
that differ from the original population
Founding Population A
Founding Population B
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Genetic Drift
Section 16-2
Sample of Original Population
Descendants
Founding Population A
Founding Population B
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EVOLUTION VERSUS GENETIC EQUILIBRIUM

• HARDY-WEINBERG PRINCIPLE ALLELE FREQUENCIES IN A
  POPULATION WILL REMAIN CONSTANT AS LONG AS FIVE
  CONDITIONS (FACTORS) REMAIN CONSTANT. GENETIC
  EQUILIBRIUM IS REACHED. (IS THE POPULATION
  EVOLVING?)

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5 CONDITIONS REQUIRED TO MAINTAIN GENETIC
EQUIIBRIUM

• RANDOM MATING
• - Select mates w/o bias
• 2. LARGE POPULATION
• - Genetic drift does not affect large pops
• 3. NO MOVEMENT INTO OR OUT OF THE POPULATION
• - no intro of new allele
• 4. NO MUTATION
• - no new allele introduced
• NO NATURAL SELECTION
• - No phenotype can have selective advantage
• DOES THIS EVER HAPPEN?????

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• In 1908, Hardy and Weinberg independently
  demonstrated that DOMINANT ALLELES DO NOT REPLACE
  RECESSIVE ALLELES IN A POPULATION!

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HARDY-WEINBERG EQUATION

• You have sampled a population in which you know
  that the percentage of the homozygous recessive
  genotype (aa) is 36. Using that 36, calculate
  the following
• The frequency of the "aa" genotype.
• The frequency of the "a" allele.
• The frequency of the "A" allele.
• The frequencies of the genotypes "AA" and "Aa."
• The frequencies of the two possible phenotypes if
  "A" is completely dominant over "a."

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• FREQUENCY OF aa GENOTYPE 36 (GIVEN)
• FREQUENCY OF a ALLELEThe frequency of aa is 36,
  which means that q2 0.36, by definition. If q2
  0.36, then q 0.6, again by definition. Since
  q equals the frequency of the a allele, then the
  frequency is 60.
• The frequency of the "A" allele. Answer Since q
  0.6, and p q 1, then p 0.4 the frequency
  of A is by definition equal to p, so the answer
  is 40.

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• The frequencies of the genotypes "AA" and "Aa."
  Answer The frequency of AA is equal to p2, and
  the frequency of Aa is equal to 2pq. So, using
  the information above, the frequency of AA is 16
  (i.e. p2 is 0.4 x 0.4 0.16) and Aa is 48 (2pq
  2 x 0.4 x 0.6 0.48).
• The frequencies of the two possible phenotypes if
  "A" is completely dominant over "a." Answers
  Because "A" is totally dominate over "a", the
  dominant phenotype will show if either the
  homozygous "AA" or heterozygous "Aa" genotypes
  occur. The recessive phenotype is controlled by
  the homozygous aa genotype. Therefore, the
  frequency of the dominant phenotype equals the
  sum of the frequencies of AA and Aa, and the
  recessive phenotype is simply the frequency of
  aa. Therefore, the dominant frequency is 64 and,
  in the first part of this question above, you
  have already shown that the recessive frequency
  is 36.

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AS NEW SPECIES EVOLVE (SPECIATION), POPULATIONS
BECOME REPRODUCTIVELY ISOLATED FROM EACH OTHER.
Section 16-3
Reproductive Isolation
results from
Isolating mechanisms
which include
produced by
produced by
produced by
which result in
Independentlyevolving populations
which result in
Formation ofnew species
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Flowchart
Section 17-4
Species
that are
in
under
under
form
in
in
can undergo
can undergo
can undergo
can undergo
can undergo
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• Divergent evolution? when 2/ more species
  originate from a common ancestor
• Ex flipper of whale and limb of human
• b. Convergent evolution? process by which
  unrelated organisms come to resemble each other
• Ex torpedo shape of shark and penguin/ wing of
  insect and bat
• c. Coevolution? process by which 2 species
  evolve in response to changes in each other over
  time