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Descent with Modification

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Title: Descent with Modification


1
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

2
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

3
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.

4
  • 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

5
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
6
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

7
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8
  • 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

9
  • 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

10
  • 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
11
  • Genotype Frequencies
  • 3 genotypes (AA, Aa, aa)
  • p2 AA
  • 2pq Aa
  • q2 aa

12
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13
  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.

14
  • If any of the Hardy-Weinberg conditions are not
    met ? microevolution occurs
  • Microevolution generation to generation change
    in a populations allele frequencies

15
  • Mutations changes in DNA
  • Point mutations
  • Gene duplication

Mutation will alter or create new alleles in a
population.
16
  • Sexual Recombination
  • Rearrange alleles into fresh combinations every
    generation

17
  1. Natural selection

Douglas fir trees only release their seeds during
fires. Fire rarely occurs in the river bottom of
this valley.
18
  • Genetic drift a change in a populations allele
    frequencies due to chance
  • bottleneck and founder effect

19
  • 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
20
  1. Founder effect few individuals become isolated
    from larger population ? certain alleles
    over/under represented

Polydactyly in Amish population
21
  • 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

22
  • Natural selection can alter frequency
    distribution of heritable traits in 3 ways
  • Directional selection
  • Disruptive (diversifying) selection
  • Stabilizing selection

23
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
24
Preserving Genetic Variation
  • Diploidy inherit 2 alleles
  • Recessive alleles less favorable
  • Heterozygote protection
  • Heterozyote Advantage
  • People hybrid for sickle cell anemia protected
    against malaria.

25
  • 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
26
  • 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)

27
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

28
Anagenesis
Cladogenesis
29
  • 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

30
  • 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

31
  • 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

32
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
33
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

34
Two main modes of speciation
35
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)
36
  • 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

37
When 2 splintered groups rejoin geographically
  • Possibilities
  • Still one species
  • Two distinct species (no interbreeding)
  • Hybrid zone

Interbreeding zone
38
  • 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

39
  • Independent development of similar features
    between 2 unrelated species
  • Similar environments
  • Analogous structures
  • Eg. wings on bees wings on birds

40
  • 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???

41
  • 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

42
  • 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)

43
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

44
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
45
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46
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

47
Evolution of Animals Body Plan
48
Evolution of Animals Body Cavities
49
Evolution of Animals Development
50
Evolution of Animals
51
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52
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)

53
Chordate Characteristics
54
Phylogeny of living chordates
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