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Biology . 18-2 Modern Evolutionary Classification. Evolutionary Classification. Linnaeus grouped species into larger taxa mainly according to visible similarities and differences . How are evolutionary relationships important in classification?. Evolutionary Classification.

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Biology l.jpg

Biology

Copyright Pearson Prentice Hall


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18-2 Modern Evolutionary Classification

Copyright Pearson Prentice Hall


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EvolutionaryClassification

  • Linnaeus grouped species into larger taxa mainly according to visible similarities and differences.

  • How are evolutionary relationships important in classification?

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Evolutionary Classification

  • Evolutionary Classification

    • Phylogeny is the study of evolutionary relationships among organisms.

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Evolutionary Classification

  • Biologists currently group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities.

  • The strategy of grouping organisms is based on evolutionary history and is called evolutionary classification.

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Evolutionary Classification

  • The higher the level of the taxon, the further back in time is the common ancestor of all the organisms in the taxon.

  • Organisms that appear very similar may not share a recent common ancestor.

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Evolutionary Classification

  • Different Methods of Classification

Mollusk

Crustaceans

Conical Shells

Appendages

Crab

Barnacle

Limpet

Barnacle

Limpet

Crab

Molted external skeleton

Tiny free-swimming larva

Segmentation

CLASSIFICATION BASED ON VISIBLE SIMILARITY

CLADOGRAM

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Evolutionary Classification

  • Superficial similarities once led barnacles and limpets to be grouped together.

Conical Shells

Appendages

Crab

Barnacle

Limpet

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Evolutionary Classification

  • However, barnacles and crabs share an evolutionary ancestor that is more recent than the ancestor that barnacles and limpets share.

  • Barnacles and crabs are classified as crustaceans, and limpets are mollusks.

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Classification UsingCladograms

  • Classification Using Cladograms

    • Many biologists now use a method called cladistic analysis.

    • Cladistic analysis identifies and considers only new characteristics that arise as lineages evolve.

    • Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters.

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Classification UsingCladograms

  • Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms.

  • Cladograms help scientists understand how one lineage branched from another in the course of evolution.

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Classification UsingCladograms

  • A cladogram shows the evolutionary relationships between crabs, barnacles, and limpets.

Crustaceans

Mollusk

Barnacle

Limpet

Crab

Molted external skeleton

Segmentation

Tiny free-swimming larva

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Similarities in DNAand RNA

  • Similarities in DNA and RNA

    • How can DNA and RNA help scientists determine evolutionary relationships?

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Similarities in DNA and RNA

  • The genes of many organisms show important similarities at the molecular level.

  • Similarities in DNA can be used to help determine classification and evolutionary relationships.

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Similarities in DNA and RNA

  • DNA Evidence

    • DNA evidence shows evolutionary relationships of species.

    • The more similar the DNA of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms.

    • The more two species have diverged from each other, the less similar their DNA will be.

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Molecular Clocks

  • Molecular Clocks

    • Comparisons of DNA are used to mark the passage of evolutionary time.

    • A molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.

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Molecular Clocks

A gene in an ancestral species

  • Molecular Clock

2 mutations

2 mutations

new mutation

new mutation

new mutation

Species

Species

Species

A

C

B

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Molecular Clocks

  • A molecular clock relies on mutations to mark time.

  • Simple mutations in DNA structure occur often.

  • Neutral mutations accumulate in different species at about the same rate.

  • Comparing sequences in two species shows how dissimilar the genes are, and shows when they shared a common ancestor.

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18-2

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18-2

  • Grouping organisms together based on their evolutionary history is called

    • evolutionary classification.

    • traditional classification.

    • cladogram classification.

    • taxonomic classification.

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18-2

  • Traditional classification groups organisms together based on

    • derived characters.

    • similarities in appearance.

    • DNA and RNA similarities.

    • molecular clocks.

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18-2

  • In an evolutionary classification system, the higher the taxon level,

    • the more similar the members of the taxon become.

    • the more common ancestors would be found in recent time.

    • the fewer the number of species in the taxon.

    • the farther back in time the common ancestors would be.

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18-2

  • Classifying organisms using a cladogram depends on identifying

    • external and internal structural similarities.

    • new characteristics that have appeared most recently as lineages evolve.

    • characteristics that have been present in the group for the longest time.

    • individual variations within the group.

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18-2

  • To compare traits of very different organisms, you would use

    • anatomical similarities.

    • anatomical differences.

    • DNA and RNA.

    • proteins and carbohydrates.

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END OF SECTION


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