Descent with Modification

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Descent with Modification

• Theme
• Evolutionary change is based on the interactions
  between populations their environment which
  results in adaptations (inherited
  characteristics) to increase fitness
• Evolution change over time in the genetic
  composition of a population

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Charles Darwin (1809-1882)

• English naturalist
• 1831 joined the HMS Beagle for a 5-year research
  voyage around the world (stopped at Galapagos
  Islands)
• 1859 published Origin of Species
• Influenced by Lamarck, Hutton Lyell, Malthus

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Darwins Theory of Natural Selection

1. Populations produce more offspring than can
   possibly survive.
2. Individuals in a population vary extensively from
   each other, mostly due to inheritance.
3. Struggle to survive individuals whose inherited
   characteristics best fit to environment leave
   more offspring than less fit.
4. Unequal ability of individuals to survive and
   reproduce leads to gradual change in pop, with
   favorable characteristics accumulating over
   generations.

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• Populations evolve, not individuals.
• Fitness is determined by the environment.
• In summary
• Natural Selection differential success in
  reproduction
• Product of natural selection adaptations of
  populations to environment

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Therefore, if humans can create substantial
change over short time, nature can over long time.
Natural Selection Artificial Selection
Nature decides Man decides
Works on individual Selective breeding
Inbreeding occurs
i.e. beaks i.e. dalmations
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Evidence for Evolution

• Biogeography
• Geographic distribution of a species
• Geographic, reproductive isolation
• Fossil Record transitional forms
• Comparative Anatomy
• Homologous structures
• Vestigial structures
• Embryonic Development
• Molecular Biology
• DNA, proteins

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• Darwins could not explain how inherited
  variations are maintained in populations - not
  trait blending
• A few years after Darwins Origin of Species,
  Gregor Mendel proposed his hypothesis of
  inheritance
• Parents pass on discrete heritable units (genes)
  that retain their identities in offspring

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• Frequencies of alleles genotypes in a
  populations gene pool remain constant from
  generation to generation unless acted upon by
  agents other than sexual recombination (gene
  shuffling in meiosis)
• Equilibrium allele and genotype frequencies
  remain constant

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• Allele Frequencies
• Gene with 2 alleles p, q
• p frequency of allele A in a population
• q frequency of allele a in a population

Note 1 p q 1 q p
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• Genotype Frequencies
• 3 genotypes (AA, Aa, aa)
• p2 AA
• 2pq Aa
• q2 aa

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1. Extremely large population size (no genetic
   drift).
2. No gene flow (isolation from other populations).
3. No mutations.
4. Random mating (no sexual selection).
5. No natural selection.

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• If any of the Hardy-Weinberg conditions are not
  met ? microevolution occurs
• Microevolution generation to generation change
  in a populations allele frequencies

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• Mutations changes in DNA
• Point mutations
• Gene duplication

Mutation will alter or create new alleles in a
population.
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• Sexual Recombination
• Rearrange alleles into fresh combinations every
  generation

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1. Natural selection

Douglas fir trees only release their seeds during
fires. Fire rarely occurs in the river bottom of
this valley.
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• Genetic drift a change in a populations allele
  frequencies due to chance
• bottleneck and founder effect

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• Bottleneck Effect genetic drift due to drastic
  reduction in population size
• Certain alleles may be over/under represented

Northern elephant seals hunted nearly to
extinction in California
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1. Founder effect few individuals become isolated
   from larger population ? certain alleles
   over/under represented

Polydactyly in Amish population
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• Gene flow genetic exchange due to migration of
  fertile individuals
• i.e. wind storm blows pollen to another field
• Reduces differences between populations
• Gain/lose alleles

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• Natural selection can alter frequency
  distribution of heritable traits in 3 ways
• Directional selection
• Disruptive (diversifying) selection
• Stabilizing selection

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Diversifying Selection eg. small beaks for small
seeds large beaks for large seeds
Stabilizing Selection eg. average human birth
weight
Directional Selection eg. beak sizes of birds
during wet/dry seasons in Galapagos
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Preserving Genetic Variation

• Diploidy inherit 2 alleles
• Recessive alleles less favorable
• Heterozygote protection
• Heterozyote Advantage
• People hybrid for sickle cell anemia protected
  against malaria.

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• Sexual selection for mating success
• Intra (within same sex) competition for mate
• Inter (out) mate choice

Sexual selection may lead to pronounced secondary
differences between the sexes
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• Remember
• Individuals are selected
• Populations evolve
• Terms
• Population localized group belonging to same
  species
• Species members of a population that can
  interbreed and produce fertile viable offspring
• Gene pool total combo of genes in a population
  at any one time
• Fixed population all members are homozygous for
  trait (usually not the case)

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Speciation origin of species

• Microevolution changes within a single gene pool
• Macroevolution evolutionary change above the
  species level
• cumulative effects of speciation over long
  periods of time

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Anagenesis
Cladogenesis
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• Anagenesis (new race)
• Phyletic evolution
• A single species gradually changes into a
  different species
• No original group left
• Evolution in single direction

• Cladogenesis (branch race)
• Branching evolution
• One species stays same, but small portion leaves
  and changes to another species
• Gene pool splits
• Original new groups
• Increase in diversity/ of species

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• Proposed by Ernst Mayr (1942)
• Species population or group of populations
  whose members have the potential to interbreed in
  nature and produce viable, fertile offspring
• Reproductively compatible
• Reproductive isolation barriers that prevent
  members of 2 species from producing viable,
  fertile hybrids

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• Prezygotic Barriers
• Impede mating/fertilization
• Types
• Habitat isolation
• Temporal isolation
• Behavioral isolation
• Mechanical isolation
• Gametic isolation

• Postzygotic Barriers
• Prevent hybrid zygote from developing into viable
  adult
• Types
• Reduced hybrid viability
• Reduced hybrid fertility
• Hybrid breakdown

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Prezygotic barriers impede mating or hinder
fertilization if mating does occur
Gametic isolation
Mechanical isolation
Behavioral isolation
Temporal isolation
Habitat isolation
Individuals of different species
Mating attempt
Fertilization
TEMPORAL ISOLATION
HABITAT ISOLATION
BEHAVIORAL ISOLATION
MECHANICAL ISOLATION
GAMETIC ISOLATION
Postzygotic barriers prevent a hybrid zygote
from developing into a viable, fertile adult
Reduced hybrid fertility
Reduced hybrid viability
Hybrid breakdown
Viable, fertile offspring
Fertilization
REDUCED HYBRID VIABILITY
REDUCED HYBRID FERTILITY
HYBRID BREAKDOWN
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Other definitions of species

• Morphological by body shape, size, and other
  structural features
• Paleontological fossil record
• Ecological niche/role in community
• Phylogenetic unique genetic history, branch on
  tree of life

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Two main modes of speciation
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Two main modes of speciation
Allopatric Speciation other homeland
Geographically isolated
Evolves by natural selection genetic drift
Eg. Galapagos finches
Sympatric Speciation same homeland
Overlapping populations within home range
Subset of population isolated from parent pop. change due to chromosomal changes nonrandom mating habitat differentiation
Eg. polyploidy in plants (oats, cotton, potatoes, wheat)
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• Emergence of numerous species from a common
  ancestor introduced into new environment
• Occurs when
• A few organisms make way to new, distant areas
  (allopatric speciation)
• Environmental change ? extinctions ? new niches
  for survivors
• Eg. Hawaiian archepelago

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When 2 splintered groups rejoin geographically

• Possibilities
• Still one species
• Two distinct species (no interbreeding)
• Hybrid zone

Interbreeding zone
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• Gradualism
• Darwin
• Slow, constant change
• Less likely

• Punctuated Equilibium
• Eldridge Gould
• Long period of minor change are interrupted by
  short bursts of significant change
• More likely

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• Independent development of similar features
  between 2 unrelated species
• Similar environments
• Analogous structures
• Eg. wings on bees wings on birds

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• REMEMBER!!
• Dear King Philip Came Over For Good Spaghetti
• Dear King Philip Crossed Over Five Great Seas
• Dear King Philip Came Over From Germany Stoned
• Your own???

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• Phylogeny evolutionary history of a species or
  group of species
• Phylogram the length of a branch reflects the
  number of changes that have taken place in a
  particular DNA sequence in that lineage

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• Cladogram diagram of evolutionary relationship
  of organisms
• Shared characteristics due to common ancestry
• Uses parsimony simplest explanation, fewest DNA
  base changes for tree (keep it simple)

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Comparison of Structures

• Homology

• Analogy

• Results from
• Adaptive radiation
• Common ancestor
• Similar origin
• Different functions
• Eg. wing of bat, human arm, dolphin flipper

• Results from
• Convergent evolution
• Different ancestors
• Different origin
• Similar functions
• Eg. wings of bird, wings of insect

• Remember
• Adaptive radiation emergence of many species
  from common ancestor
• Convergent evolution unrelated species
  independently evolve similarities when adapting
  to similar environments

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Major events during each Era

• Precambrian microscopic fossils (stromatolites)
• Photosynthesis, atmospheric O2
• Eukaryotes (endosymbiont theory)
• Paleozoic Cambrian Explosion
• Plants invade land, many animals appear
• Permian Extinction (-96 species)
• Mesozoic Age of Reptiles, dinosaur, plants
• Formation of Pangaea supercontinent
• Cretaceous Extinction asteroid off Mexicos
  coast
• Cenozoic primates

Note All end with major extinction start with
adaptive radiation
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Evolution of Plants

• Non-Vascular (liverworts, hornworts, mosses)?
  Seedless Vascular (ferns) ? Seed Vascular
  (gymnosperms, angiosperms)
• Mosses Gametophytes dominant form
• Ferns 1st with vascular tissue (xylem, phloem
• wet environment (fertilization in water)
• Sporophyte dominant form
• Gymnosperms naked seeds on cones
• Conifers
• Angiosperms flowering plants

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Evolution of Animals Body Plan
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Evolution of Animals Body Cavities
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Evolution of Animals Development
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Evolution of Animals
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Evolution of Animals

• Porifera (sponge)
• Cnidarian (jellyfish, hydra)
• Flatworms (planaria)
• Mollusc
• Gastropod (snail), bivalve (clams), cephalopod
  (octopus)
• Annelid (earthworm)
• Arthropods (insects, crustaceans)
• Echinoderms (spiny skin starfish, sea
  urchins)
• Chordates (vertebrates)

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Chordate Characteristics
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Phylogeny of living chordates