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Phylogeny and Systematics, Ch 25, U208PP

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Title: Phylogeny and Systematics, Ch 25, U208PP


1
Phylogeny and Systematics, Ch 25, U208PP
2
  • This chapter describes how biologists trace
    phylogeny (the evolutionary history of a species
    or group of related species)
  • phylogeny used to draw heavily on the fossil
    record
  • Biologists now also use systematics, an
    analytical/mathematical approach
  • systematics may use computer analysis of
    molecular sequences to infer relationships
    between groups

Our goal is to accurately reconstruct the
relationships among different parts of Darwins
tree of life
How good is this evidence?
To do that, we are going to consider fossil,
morphological, and molecular evidence
3
  • Biologists draw on the fossil record
  • Which provides information about ancient organisms

Figure 25.1
4
The Fossil Record
  • Sedimentary rocks
  • Are the richest source of fossils
  • Are deposited into layers called strata

Figure 25.3
5
So you want to become a fossil? Here are the
steps
  • Die, but die in the right place
  • Do not be decomposed or scavenged
  • Chemically change so that your hard parts
    fossilize
  • Do not be damaged by geologic processes, like
    earthquakes or erosion
  • Become exposed after thousands or millions of
    years
  • Be found by someone competent to understand you
    are a valuable fossil and not just some dumb ol
    rock.

6
  • Though sedimentary fossils are the most common
  • Paleontologists study a wide variety of fossils

7
  • The fossil record
  • Is based on the sequence in which fossils have
    accumulated in such strata
  • Fossils reveal
  • Ancestral characteristics that may have been lost
    over time
  • Fossils CAN show
  • Location, age of fossil, size and body
    organization
  • But frequently CANT show
  • Internal anatomical changes
  • Behavior
  • Changes in body function
  • Molecular changes/alleles
  • color

Yea. And we have something else to be cautious
of
Whoa. So what you are saying is that the fossil
record may be incomplete (since not everything
fossilized or survived as a fossil to be
discovered) and that even existing fossils have
limitations?
8
Sorting Homology from Analogy
  • A potential misconception in constructing a
    phylogeny
  • Is similarity due to convergent evolution, called
    analogy, rather than shared ancestry

9
  • Convergent evolution occurs when similar
    environmental pressures and natural selection
  • Produce similar (analogous) adaptations in
    organisms from different evolutionary lineages

Figure 25.5
10
  • Analogous structures or molecular sequences that
    evolved independently
  • Are also called homoplasies

THESE DO NOT REFLECT EVOLUTIONARY RELATIONSHIPS!
11
Morphological and Molecular Homologies
  • In addition to fossil organisms
  • Phylogenetic history can be inferred from certain
    morphological and molecular similarities among
    living organisms
  • In general, organisms that share very similar
    morphologies or similar DNA sequences
  • Are likely to be more closely related than
    organisms with vastly different structures or
    sequences

12
  • Currently, systematists use
  • Morphological, biochemical, and molecular
    comparisons to infer evolutionary relationships

Figure 25.2
13
Evaluating Molecular Homologies
  • Systematists use computer programs and
    mathematical tools
  • When analyzing comparable DNA segments from
    different organisms

14
  • Phylogenies are based on common ancestries
    inferred from fossil, morphological, and
    molecular evidence

15
  • Concept 25.2 Phylogenetic systematics connects
    classification with evolutionary history
  • Taxonomy
  • Is the ordered division of organisms into
    categories based on a set of characteristics used
    to assess similarities and differences

16
Binomial Nomenclature
  • Binomial nomenclature
  • Is the two-part format of the scientific name of
    an organism
  • Was developed by Carolus Linnaeus
  • Administered today by international scientific
    organizations, r.g., International Code of
    Botanical Nomenclature
  • The binomial name of an organism or scientific
    epithet
  • Is latinized
  • Is the genus and species

17
Canis familiaris
Escherichia coli
Quercus niger
Tyrannosaurus rex
Homo sapiens
Staphlococcus aureus
Lymantria dispar
Quercus rubra
18
Hierarchical Classification
  • Linnaeus also introduced a system
  • For grouping species in increasingly broad
    categories

Figure 25.8
19
Linking Classification and Phylogeny
  • Systematists depict evolutionary relationships
  • In branching phylogenetic trees

Figure 25.9
20
  • Each branch point
  • Represents the divergence of two species

21
  • Deeper branch points
  • Represent progressively greater amounts of
    divergence
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