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What Homologies tell us

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Title: What Homologies tell us


1
What Homologies tell us
  • Similarities in structure and chemistry provide
    powerful evidence that all living things evolved
    from a common ancestor
  • Darwin Concluded
  • Living organisms evolved through gradual
    modifications of earlier forms ? descent with
    modification

2
What Similarities tell us
  • Two types of evolution can account for homologous
    AND analogous structures
  • Convergent evolution
  • Divergent evolution

3
What Similarities tell us
  • Divergent evolution two species evolve from a
    common ancestor (speciation)
  • They share similarities in anatomy, biochemistry,
    and embryology due to common ancestry
  • Explains homologous structures

4
What Similarities tell us
  • Convergent two species apparently becoming more
    similar
  • Two species have adapted in similar ways to
    similar environmental conditions
  • NOT due to common ancestry
  • Explains analogous structures

5
Convergent Evolution
  • Ocotillo from California and allauidi from
    Madagascar have evolved similar mechanisms for
    protecting themselves

6
Convergent Evolution
  • Adaptive radiation of anoles has occurred on the
    islands of the Greater Antilles in a convergent
    fashion. On each island, different species of
    the lizards have adapted to living in different
    parts of trees, in strikingly similar ways.

7
Convergent Evolution
8
Convergent Evolution
9
Diversity of Life
  • Fitness
  • Physical traits and behaviors that enable
    organisms to survive and reproduce in their
    environment arises from adaptation.
  • Adaptation allows species to be better suited to
    their environment and therefore can survive and
    reproduce.

10
Evolution on Different Scales
  • Microevolution generation-to-generation change
    in a populations allele frequencies
  • Macroevolution origin of new taxonomic groups
    speciation

11
4 Driving Forces behind Evol.
  • Mutation
  • Any change in the original DNA
  • ONLY ultimate source of variation in a population
  • Gene Flow
  • Movement of genes either into or out of a
    population
  • Migration Immigration (add alleles) and
    Emigration (subtract alleles)

12
4 Driving Forces behind Evol.
  • Genetic Drift
  • Change in the allele frequency in a small
    population by chance alone
  • Bottleneck Effect
  • Founder Effect

13
4 Driving Forces behind Evol.
  • Genetic Drift
  • Bottleneck Effect population undergoes a high
    mortality rate genetic variation decreases
    dramatically
  • Ex Cheetahs

14
Genetic Drift Bottleneck Effect
15
4 Driving Forces behind Evol.
  • Genetic Drift
  • Founder Effect few individuals leave a large
    population to start their own gene pool is very
    limited
  • Ex polydactyly in PA Amish

16
Genetic Drift Founder Effect
17
Genetic Drift Founder Effect
18
4 Driving Forces behind Evol.
  • Selection
  • Natural differential success in the
    reproduction of different phenotypes resulting
    from the interaction of organisms with their
    environment
  • Nature does the selecting

19
4 Driving Forces behind Evol.
  • Selection (Natural)
  • Resistance overuse of insecticides and
    antibiotics have bred resistant species of bugs
    and germs

20
4 Driving Forces behind Evol.
  • Selection
  • Artificial breeding of domesticated plants and
    animals
  • Humans intentionally do the selecting
  • Cabbage, cauliflower, Brussels sprouts,
    kale, kohlrabi and broccoli have a
    common ancestor in one species of wild
    mustard

21
4 Driving Forces behind Evol.
  • Problems with artificial selection not enough
    genetic variation

22
4 Driving Forces behind Evol.
  • Selection (Sexual)
  • Intrasexual selection selection within the same
    sex (competition, usually between males
  • Competition, usually between males
  • Exaggerated anatomy

Bighorn Sheep
Rocky Mountain Elk
Five-horned Rhinoceros Beetles
Stagbeetles
23
4 Driving Forces behind Evol.
  • Selection (Sexual)
  • Intersexual selection one sex selects mate
    based on phenotypes
  • Exaggerated anatomy

24
  • Selection can influence populations in three
    major ways
  • Directional Sel.
  • Stabilizing Sel.
  • Disruptive (diversifying) Sel.

25
Directional Selection
  • Environment selects against one phenotypic
    extreme, allowing the other to become more
    prevalent

26
Disruptive Selection
  • Environment selects against intermediate
    phenotype, allowing both extremes to become more
    prevalent

27
Stabilizing Selection
  • Environment selects against two extreme
    phenotypes, allowing the intermediates to become
    more prevalent

28
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29
Key Points
  1. Natural selection does not cause genetic changes
    in individuals.
  2. Natural selection acts on individuals evolution
    occurs in populations.
  3. Evolution is a change in the allele frequencies
    of a population, owing to unequal success at
    reproduction among organisms bearing different
    alleles.
  4. Evolutionary changes are not good nor
    progressive in any absolute sense.

30
Evolutionary Theory
  • Foundation on which the rest of the biological
    science is built. Collection of carefully
    reasoned and tested hypotheses about how
    evolutionary change occurs.

31
Speciation
  • What is a species?
  • Biological definition a group of closely related
    organisms (population) that can interbreed to
    produce fertile, viable offspring

32
Speciation
  • Why cant/dont populations interbreed?
  • Prezygotic barriers
  • Postzygotic barriers

33
Prezygotic Barriers
  • Ecological (habitat) isolation pops live in
    different habitats and do not meet
  • Parasites generally dont transfer hosts
  • Temporal isolation active or fertile at
    different times
  • Flowering plants pollinate on different days or
    different times of the day

34
Prezygotic Barriers
  • Behavioral isolation differences in activities
  • Mating calls or actions are different

35
Prezygotic Barriers
  • Mechanical isolation mating organs do not fit
    or match
  • Enough said
  • Gametic isolation gametes cannot combine
  • Sperm destroyed in different vaginal cavity
  • Sperm and egg dont fuse due to different
    membrane proteins

36
Postzygotic Barriers
  • Hybrid inviability hybrid zygotes fail to
    develop or reach sexual maturity
  • Hybrid infertility hybrids fail to produce
    functional gametes

37
Summary
  • 2 or more mechanisms may occur at once
  • Ex Bufo americanus and Bufo fowleri are
    ecologically, temporally, and behaviorally
    isolated
  • Bufo americanus breeds in early spring in small,
    shallow puddles or nearby dry creeks
  • Bufo fowleri breeds in late spring in large pools
    and streams
  • Their mating calls also differ

38
Limitations of Biological Species Concept
  • How do you classify organisms that
  • have the potential to interbreed, but do not do
    so in nature?
  • do not reproduce sexually?
  • exist only as fossils?
  • Alternative species concepts (ecological,
    pluralistic, morphological, genealogical) help
    address limitations

39
Modes of Speciation
  • Allopatric (Greek, allos other Latin, patria
    homeland)
  • Speciation due to geographic separation
  • Barrier stops gene flow between populations
  • Evolutionary change acts independently on each
    pop to establish reproductive barriers

40
  • Mitochondrial DNA analysis has shown that certain
    tamarin monkey pops (those separated by wide
    rivers) are diverging toward speciation
  • Where the Amazon is very wide, tamarins on one
    side are brown, but on the other side are white.
    Where the Amazon is narrow, tamarins of both
    colors are found on either side

41
Allopatric Speciation
  • Birds can move freely across the gorge of the
    Grand Canyon squirrels cannot
  • Two species arose when their original pop was
    disrupted by the carving of the canyon

42
  • A. harrisi
  • A. leucurus

43
Allopatric Speciation
  • If not given enough time, speciation will not
    occur
  • Also, even if they do
    come back together, they
    need to interbreed to be the same
    species

44
Allopatric Speciation
  • Figure 24.11
  • Adaptive Radiation evolution of
    many diversely-adapted species from a
    common ancestor
  • Ex Hawaiian archipelago

45
Sympatric Speciation
  • Sympatric (Greek, sym together Latin, patria
    homeland)
  • Speciation occurs in populations that share a
    habitat
  • Results from
  • Ecological isolation
  • Polyploidy (number of sets of chromosomes
    increases)

46
Sympatric Speciation
  • Polyploidy (number of sets of chromosomes
    increases)
  • A result of accidents in meiosis

47
Will Speciation Occur?
  • p q 1
  • p2 2pq q2 1
  • Will speciation occur? You tell me!
  • Hardy-Weinberg PPT 1
  • Hardy-Weinberg PPT 2

48
Evolutionary Time Scales
  • Evolution can take a long time or can occur
    relatively quickly
  • Gradualism
  • Punctuated Equilibrium

49
Evolutionary Time Scales
  • Gradualism big evolutionary changes are the
    result of many small ones over a long period of
    time

50
Evolutionary Time Scales
  • Punctuated Equilibrium speciation occurs fairly
    rapidly then remain constant

51
Evolutionary Novelties
  • Unique and highly specialized organs seem to
    complicated to have been naturally selected
  • Ex eyes are really just photoreceptors some are
    more developed, but all do the basic function
    receive light

52
Evolutionary Novelties
53
Evo-devo
  • Evolutionary development
  • A field of interdisciplinary research that
    examines how slight genetic divergences can
    become magnified into major morphological
    differences between species

54
Evo-devo
  • By blocking expression of one gene, researchers
    forced a chickens foot to develop to resemble a
    ducks foot
  • Two embryos from the same animal

55
Evo-devo
  • Left, a normal chicken leg will develop
  • Right, a normal duck leg will develop from a
    chicken embryo
  • Chicken leg scaled with 4 digits
  • Duck leg smooth and webbed
  • Duck legs, due to one genetic evolutionary
    difference, help ducks do many things chickens
    cannot, like swim
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