Phylogeny and Systematics, Ch 25, U208PP

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Phylogeny and Systematics, Ch 25, U208PP
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• 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
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• Biologists draw on the fossil record
• Which provides information about ancient organisms

Figure 25.1
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The Fossil Record

• Sedimentary rocks
• Are the richest source of fossils
• Are deposited into layers called strata

Figure 25.3
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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.

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

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• 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?
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Sorting Homology from Analogy

• A potential misconception in constructing a
  phylogeny
• Is similarity due to convergent evolution, called
  analogy, rather than shared ancestry

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

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

THESE DO NOT REFLECT EVOLUTIONARY RELATIONSHIPS!
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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

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

Figure 25.2
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Evaluating Molecular Homologies

• Systematists use computer programs and
  mathematical tools
• When analyzing comparable DNA segments from
  different organisms

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

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• 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

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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

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Canis familiaris
Escherichia coli
Quercus niger
Tyrannosaurus rex
Homo sapiens
Staphlococcus aureus
Lymantria dispar
Quercus rubra
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Hierarchical Classification

• Linnaeus also introduced a system
• For grouping species in increasingly broad
  categories

Figure 25.8
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Linking Classification and Phylogeny

• Systematists depict evolutionary relationships
• In branching phylogenetic trees

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

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• Deeper branch points
• Represent progressively greater amounts of
  divergence