Download Example - Harrison High School

SB5
Chapters 14, 15, & 16
Chapter 15
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All organisms have evolutionary
adaptations
 Inherited characteristics that enhance
their ability to survive and reproduce
Example: The blue-footed booby of the
Galápagos Islands has features
that help it succeed in its
environment
▪ Large, webbed feet help
propel the bird through
water at high speeds
▪ A streamlined shape, large tail, and
nostrils that close are useful for diving
▪ Specialized salt-secreting glands manage
salt intake while at sea
Aristotle and the Judeo-Christian culture believed that species
were fixed.
 Fossils suggested that life forms change.
 Early 1800s Jean Baptiste Lamarck, a French invertebrate
specialist, studied fossils to learn about different invertebrates.
 He was surprised by the similarities between the existing
animals that he studied.
 He also noticed that fossils showed traits changing over time.
For example, he noticed that giraffes’ necks were getting longer
and longer from generation to generation. He theorized that
this trait developed as giraffes stretched their necks for higher
leaves to avoid competition with shorter animals.
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English naturalist who sailed on the HMS
Beagle
Mission of 5-yr voyage – map the coast of
South America
Darwin’s role – collect biological and
geological samples
Inspirational reading – Charles Lyell’s book
proposing that the earth was millions of years
old
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Similarities between living things and fossil
organisms
Diversity of life on the Galapagos Islands,
such as blue-footed boobies and giant
tortoises
▪ Visited 4 islands in the chain; noticed each island had
slightly different varieties of animal
▪ Discovered many new species that were not found in S
America
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Darwin became convinced that the Earth was
old (as Lyell said in the book he was reading).
 He suggested that the Earth is continually
changing.
 He concluded that living things also change or
evolve over generations.
 He also stated that living species descended from
earlier life-forms: descent with modification.
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He believed that new species could appear
gradually through small changes in traits.
 He was unsure how this process would work.
 He turned to animal breeders for help.
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Breeders selected desired traits in pigeons
and bred them. (We called this selective
breeding in the Genetics Unit.) Darwin called
this practice artificial selection.
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Darwin explained that if humans could
change species by artificial selection, then
perhaps nature could do the same thing over
time.
He concluded that this is how new species
develop naturally over time…natural
selective breeding.
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Darwin proposed that natural selection is the
mechanism of evolution.
Natural selection – NATURE’s way of selective
breeding
Four Basic Principles:
 Organisms in a population show variations.
 Variations can be passed down to offspring.
 Organisms produce more offspring than resources
can support.
 Variations that increase survival also increase the
likelihood of reproduction and inheritance.
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The favorable characteristics are passed
down to offspring who are likely to survive
due to the favorable characteristic.
Population size increases due to favorable
characteristics in offspring.
Over time, whole populations change to
include the favorable characteristic. Enough
changes can give an entirely new species.
Natural Selection
Fossil Record, Biogeography, Comparative Anatomy, Comparative
Embryology, and Molecular Biology
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Fossils offer evidence for evolution:
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Hominid skull
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Petrified trees
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Fossilized organic matter in a leaf
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Scorpion in amber
• Many fossils link
early extinct species
with species living
today
– These fossilized hind
leg bones link living
whales with their
land-dwelling
ancestors
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Continental drift is the slow, incessant
movement of the Earth’s crustal plates on the
hot mantle.
Eurasian
Plate
North
American
Plate
African
Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Split
developing
Indo-Australian
Plate
Antarctic Plate
Edge of one plate being pushed over edge of
neighboring plate (zones of violent geologic events)
CENOZOIC
Eurasia
Africa
MESOZOIC
Antarctica
PALEOZOIC
Millions of years ago
Crustal plates have shifted
over millions of years to
significantly change the
layout of the globe.
India
South
America
Laurasia
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Homologous
structures:
anatomically
similar structures
inherited from a
common ancestor
Forelimbs of
vertebrates are
adapted for
different uses, but
they have the
similar bones.
Human
Cat
Whale
Bat
 Vestigial structure:
reduced forms (smaller)
of functional structures
in other organisms
 Example: Human
appendix; structure is
important for digestion
in many mammals but
of limited use in humans
and apes
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Vertebrate embryos
exhibit homologous
structures during
certain phases of
development.
Example: Pharyngeal
pouches
 Develop into gills in fish
 Develop into ears, jaws,
and throats in
mammals, birds, and
reptiles
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Darwin’s idea of natural selection and the
evidence of comparative anatomy has lead
scientists to observe evolution in action.
Example: Evolutionary adaptations have
been observed in many populations of birds
and insects
 Camouflage adaptations
Example: Insecticide
resistance
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
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Modern synthesis of evolution ideas connects
Darwin’s theory of natural selection with
population genetics
 So…what’s population genetics?
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Populations are the units of evolution.
A species is a group of populations whose
individuals can interbreed and produce fertile
offspring.
 Human populations tend to concentrate locally, as
this satellite photograph of North American
shows
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Microevolution is change in a
population’s gene pool over
time.
 A gene pool is the total
collection of genes in a
population at any one time.
 Microevolution involves a
change in the relative frequencies
of alleles in a gene pool.
▪ Example: Bug color ratio (frequency
of alleles)
What is the ratio of graybrown to yellow-brown
to dark brown bugs?
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The Hardy-Weinberg principle states that
evolution (change in the frequency of alleles) will
not occur unless acted upon by forces that cause
change.
 Connection to meiosis: the shuffling of genes
(crossing over, etc.) during sexual reproduction does
not alter the proportions of different alleles in a gene
pool
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When allelic frequency remains constant, a
population is in Hardy-Weinberg equilibrium.
 We can map alleles in a population to observe if
Hardy-Weinberg equilibrium exists.
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The population is very large
The population is isolated
Mutations do not alter the gene pool
Mating is random
All individuals are equal in reproductive
success
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Hardy (English mathematician) and Weinberg
(German physician) developed an equation to
show mathematically that random mating
will not cause changes in allele frequencies.
 EQUATION:
p2 + 2pq + q2 = 1
 frequency of dominant + frequency of recessive = 1
 p+q=1
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p2 = pp= homozygous dominant genotype
pq = heterozygous genotype
q2 = qq = homozygous recessive genotype
 EQUATION:
p2 + 2pq + q2 = 1
 Remember: p +q = 1
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Assume you have the following genotypes in
gold fish crackers: FF, Ff, and ff.
Mating is random. Any fish could mate with any
other fish.
F and f are the only two alleles from fish color.
 F = brown; FF and Ff are brown fish.
 f = gold; ff = gold fish
 EQUATION: p2 + 2pq + q2 = 1
 Remember: p +q = 1
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Example: Let’s say that you’ve calculated that
you have 16% ff fish. We can use the equation to
calculate the frequency of the homozygous
dominant and the heterozygous alleles.
Solved on whiteboard in class!
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Fishy Frequencies Lab in Class!
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Microevolution: change in frequencies of
alleles in a gene pool
 Example: if blue eyes began to disappear in the
population.
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Remember, the Hardy-Weinberg principle
says that reproduction and variations in
meiosis won’t cause microevolution.
Microevolution only occurs when a force acts
on the population to cause the changes.
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Genetic drift is a change in a gene pool due to
chance.
 In large populations, enough organisms are
reproducing with random selection of alleles to
prevent changes in the gene pool.
 In smaller populations, random selections could
reduce the diversity by mere chance.
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Extreme genetic drift can cause the bottleneck
effect.
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Bottleneck Effect: a
population dwindles
to a very low number
and then rebounds
 Small population gives
little diversity.
 Little diversity
reproduces little
diversity.
 Example: African
cheetahs – so
genetically similar that
they appear to be
inbred
Original
population
Bottlenecking
event
Surviving
population
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Founder Effect: a small segment of the
population moves to a separate area
 Separate segment may have traits that are
uncommon to the original population
 Uncommon traits become common in offspring in
the new population
 Can result in large genetic variability from one
segment of the population to another
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Natural selection acts to select individuals who
are the best adapted for survival and
reproduction.
 Those who lack these traits often die before
reproducing.
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Natural selection results in the accumulation of
traits that adapt a population to its environment
 If the environment should change, natural selection
would favor traits adapted to the new conditions.
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Phenotypic variation may be environmental
or genetic in origin.
Only genetic changes will result in
evolutionary adaptations as only genes are
passed to offspring.
 Example: Environment may cause a tan, but tans
are not passed down to offspring. Population skin
color will only become darker if darker skin color
genes become more common in offspring.
Frequency of
individuals
Original
population
Phenotypes (fur color)
Original
population
Evolved
population
Stabilizing selection
Directional selection
Diversifying selection
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Directional Selection:
extreme version of a trait
makes the organism more fit
for survival and reproduction
 Example: Peppered moth –
until mid-1850s moths were
light colored in England. By
early 1900s, nearly all were
dark colored. The darker the
moth, the better it blended
into the sooty surroundings of
the industrial pollution
Luck y for the moth species
that it had a darker allele to
begin favoring.
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Low genetic variability may reduce the
capacity of a species to survive as humans
continue to alter the environment.
 Example: African cheetah – diversity was
decreased by bottleneck effect which resulted in
fewer alleles (as if they’d been inbred)
 Fewer alleles = reduced capacity to adapt to
environmental challenges
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Sexual selection leads to the evolution of
secondary sexual characteristics
 These may give individuals an advantage in
mating.
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Natural selection cannot fashion perfect
organisms.
 Historical constraints
 Adaptive compromises
 Chance events
 Availability of variations
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The excessive use of
antibiotics is leading to
the evolution of antibioticresistant bacteria
 Example:
Mycobacterium
tuberculosis
 They aren’t perfect, but the
are perfectly annoying to
the CDC.