Download 18-2 Modern Evolutionary Classification

Chapter 18 Classification (18-2)
Sometimes due to convergent evolution, organisms
that are quite different from each other evolve
similar body structures.
 Biologists now group organisms into categories
that represent limes of evolutionary descent, not
just physical similarities.
 This strategy of grouping organisms together based
on their evolutionary history is called evolutionary
classification.
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Characteristics that appear in recent parts of a
lineage but not in its older members are called
derived characters.
Derived characters are used to construct a
cladogram, a diagram that shows the evolutionary
relationship among a group of organisms.
Chapter 18 Classification (18-2)
Because DNA and RNA are so similar across all
forms of life, these molecules provide an excellent
way of comparing organisms at their most basic
level—their genes.
 The genes of many organisms show important
similarities at the molecular level. These
similarities can be used as criteria to help
determine classification.
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A molecular clock uses DNA comparisons to
estimate the length of time that two species have
been evolving independently.
Neutral mutations accumulate in the DNA of
different species at about the same rate