Transcript 18.2 Modern Evolutionary Classification

18.2 Modern Evolutionary
Classification
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Which similarities are most important?
Evolutionary classification
Classification using cladograms
Similarities in DNA and RNA
Molecular clocks
Which similarities are most
important?
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Based on how Linnaeus grouped organisms
(physical characteristics), it would be difficult to
determine which characteristics you base their
name off of.
For example, would he group dolphins with fish
because they live in water and have fins, or
would they be mammals because they breath air
and feed their young milk?
Evolutionary Classification
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Phylogeny: the study of evolutionary relationships
among organisms, Darwin gave rise to this study.
Biologists now group organisms into categories that
represent lines of evolutionary descent, or phylogeny,
not just physical similarities.
Evolutionary classification: the strategy of grouping
organisms together based on their evolutionary history.
Classification Using Cladograms
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Cladistic analysis: identifies and considers only those
characteristics of organisms that are evolutionary
innovations
Derived characters: characteristics that appear in recent
parts of a lineage but not in its older members.
Cladogram: a diagram that shows the evolutionary
relationships among a group of organisms.
Cladograms, cont.
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They are useful tools that help scientists
understand how one lineage branched from
another in the course of evolution, kind of like
a family tree.
Similarities in DNA and RNA
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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.
The more similar the DNA sequence in two
species, the more recently they had a common
ancestor.
Molecular Clocks
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Molecular clock: uses DNA comparisons to estimate
the length of time that two species have been evolving
independently.
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This process relies on mutations that occur.
The degree of dissimilarities is an indication of how
long ago species shared a common ancestor.
This process can be difficult because each genome
contains more than one “clock” because of the many
different genes.