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AP Test Evolution/Classifcation
Review
Evolution
• Evolution is genetic change in a population
over time.
• Charles Darwin was the first scientist to
propose the theory of evolution, in 1859.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Darwin observed:
– similarities between living and fossil organisms
– the diversity of life on the Galápagos Islands,
such as finches (birds) and giant tortoises
Figure 13.1A
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• Darwin concluded that:
– The Earth was old and constantly changing (4.6
billion years old)
– Living things also change (evolve) over
generations.
– Living things are related to animals and plants
that used to exist but are now extinct.
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Evidence for Evolution
• Fossils
• Biogeography
• Comparative Anatomy
• Comparative Embryology
• Molecular Biology
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Natural Selection
• Darwin concluded that individuals best
suited for a particular environment are
more likely to survive and reproduce
than those less well adapted
• Aka: survival of the fittest (giraffe example)
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• Darwin saw natural selection as the basic
mechanism of evolution
– As a result, the proportion of individuals with
favorable characteristics increases
– Populations gradually change in response to the
environment
– Phenotypes that are better reproduce more,
eventually, better genotypes become more
common.
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• Darwin also saw that when
humans choose organisms
with specific characteristics as
breeding stock, they are
performing the role of the
environment
– This is called artificial
selection
– Example of artificial
selection in plants: five
vegetables derived from
wild mustard
Figure 13.4A
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13.7 Microevolution
• A gene pool is the total collection of genes in a
population at any one time
• Microevolution is a change in the relative
frequencies of alleles in a gene pool
• New mutations are constantly being generated
in a gene pool, by accident or as a response to
environmental changes.
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What causes evolution?
• Genetic drift
• Bottleneck Effect
• Founder Effect
• Gene Flow
• Mutation
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Genetic Drift
• Genetic drift is a
change in a gene pool
due to chance
– Genetic drift can
cause the bottleneck
effect: an event that
drastically reduces
population size
(fire, flood,
earthquake)
Original
population
Bottlenecking
event
Surviving
population
Figure 13.11A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Genetic drift…
• If a population is very diverse and something
bad happens, at least a few individuals will
survive.
• These individuals will then reproduce and the
species will evolve, or change.
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– The founder effect is when some individuals
leave a population and start living somewhere
new.
– Only a few people or animals leave, and the new
population will be closely related to due lack of
genetic diversity.
Figure 13.11B, C
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• Gene flow can change a gene pool due to the
movement of genes into or out of a population
(new organisms move in or leave)
• Mutation changes alleles, these are random
changes in DNA that can create new proteins or
new characteristics.
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13.8 Hardy-Weinberg Equilibrium
• Showing that evolution has to happen by
showing that characteristics in nature are
always changing...
• Hardy-Weinberg equilibrium states that the
shuffling of genes during sexual reproduction
does not alter the proportions of different
alleles in a gene pool
• Populations are always evolving and not
usually in equilibrium.
Figure 13.8A
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13.10 Five conditions are required for HardyWeinberg equilibrium
• 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
• ***This does not happen in nature!
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The Equation
• p2 + 2pq + q2 = 1
• p+q=1
• p = frequency of the dominant allele in the population (A)
q = frequency of the recessive allele in the population (a)
p2 = percentage of homozygous dominant individuals (AA)
q2 = percentage of homozygous recessive individuals (aa)
2pq = percentage of heterozygous individuals (Aa)
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MACROEVOLUTION
15.1 The fossil record chronicles macroevolution
• Macroevolution consists of the major changes
in the history of life
– The Earth is 4.6 billion years old
– Life appeared 3.8 billion years ago: as single
celled prokaryotic bacteria
– Around 500 million years ago, simple marine
animals and plants had evolved
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15.2 Radiometric Dating
• Radiometric (or carbon) dating is based on the
measurement of certain radioactive isotopes
• Scientists can measure how much carbon is left
in a fossil, and can then determine how old that
fossil is.
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15.6 Adaptations
• A structure that evolved in one context and was
later adapted to another function is referred to
as exaptation.
– Example: Dinosaurs evolved feathers as
insulation against extreme temperatures, as
birds evolved from small dinosaurs, feathers
changed through natural selection to give flight.
Figure 15.6
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15.9 Phylogeny
• Phylogeny is the evolutionary history of a group
of organisms.
• Biologists construct phylogenic trees, which are
diagrams that trace evolutionary relationships.
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15.10 Systematists classify organisms by phylogeny
• Reconstructing phylogeny is part of
systematics, the study of biological diversity
and classification.
• Taxonomists assign a two-part name to each
species (binomial nomenclature)
– The first name, the genus, covers a group of
related species (but they can’t breed!) Ex: Homo
– The second name refers to a species within a
genus Ex: sapiens
– Another Example: Canis familiaris (italics,
genus capitalized, species not)
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A review of taxonomy
• Taxonomy is the system of classifying living
organisms.
• Kings = Kingdom (Anamalia)
• Play = Phylum (Chordata)
• Chess = Class (Mammalia)
• On = Order (Primates)
• Funny = Family (Hominidae)
• Green = Genus (Homo)
• Squares = Species (sapiens)
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• A newer system recognizes two basically
distinctive groups of prokaryotes
– The domain Bacteria
– The domain Archaea
• A third domain,
the Eukarya,
includes all
kingdoms of
eukaryotes
BACTERIA
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ARCHAEA
EUKARYA
Earliest
organisms
Figure 15.14B
15.11 Homology vs. Analogy
• Homologous structures are evidence that
organisms have evolved from a common ancestor
(human arm, whale flipper)
• In contrast, analogous similarities are evidence
that organisms from different evolutionary lineages
have undergone convergent evolution (shark and
dolphin)
– Their resemblances have resulted from living in similar
environments
– Example: A bat wing and a bee wing (they are NOT
homologous, they are analogous)
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15.12 Molecular Biology
• Systematists increasingly use molecular
techniques to
Human
Chimpanzee
Gorilla
Orangutan
– classify
organisms
– develop
phylogenetic
hypotheses
– Protein sequences, DNA, and RNA of different
organisms are compared to determine
relationships.
Figure 15.12B
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15.13 Cladistic Analysis
• Clades are evolutionary branches that consist of
a common ancestor and all the organisms that
evolved from it.
• A phylogenic tree based on cladistic analysis is
called a cladogram.
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Quick Review Key terms
• Phylogeny is the evolutionary history of a
species or group of species.
• Systematics is the analytical approach to
understanding the diversity and relationships of
organisms.
• Molecular Systematics compares DNA and
RNA of different organisms to determine
evolutionary relationships
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Reproductive Barriers
• Reproductive Barriers prevent members of
different species from producing viable, fertile
offspring. (there are 2 types)
• 1. Prezygotic barriers: impede mating or hinder
fertilization if mating does occur (BEFORE
zygote forms)
• 2.Postzygotic barriers: prevent a hybrid zygote
from developing into a viable, fertile adult
(AFTER zygote forms) (Ex: Mule)
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Prezygotic Barriers
• 1. Habitat isolation: 2 species live in different
habitats and don’t see each other
• 2. Temporal isolation: 2 species breed at different
times of the day or year
• 3. Behavioral isolation: courtship rituals are species
specific, and don’t attract other species
• 4. Mechanical isolation: the sexual pieces don’t fit
together
• 5. Gametic isolation: even if sex occurs, the egg and
sperm can’t meet
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Postzygotic barriers
• 1. Reduced hybrid viability: hybrid babies die
before reaching reproductive age
• 2. Reduced hybrid fertility: hybrid babies are
sterile and can’t reproduce
• 3. Hybrid breakdown: first generation babies
can breed, but their children are infertile (F2)
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How do new species form?
• Allopatric speciation: “other country,” a
population is geographically divided into 2
isolated subpopulations, which eventually
become 2 new species
• Sympatric speciation: “same country,” 2 new
species develop in the same area
– Mutations such as polyploidy (extra set of
chromosomes)
– Habitat differentiation
– Sexual selection
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Adaptive Radiation
• Adaptive radiation: the evolution of many
diversely adapted species from a common
ancestor upon introduction to various new
environmental opportunities and challenges
• Example: Hawaiian plants
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Extras
• Punctuated equilibrium: lots of new species
appear all at once in history (Cambrian
explosion)
• Kin Selection: refers to strategies in evolution
that favor the reproductive success of an
organism's relatives, even at a cost to their own
survival. (Altruistic Behavior)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings