Download Modern Taxonomy - Fall River Public Schools

Modern Evolutionary
Classification
Objectives
Identify the purpose of cladograms
Evolutionary Classification
Phylogeny is the study of the evolutionary
relationships among organisms
Biologists now group organisms into
categories that represent lines of
evolutionary descent, not just physical
similarities
Evolutionary classification is the strategy of
grouping organisms together based on their
evolutionary history
Evolutionary Classification
Species within a genus are more closely
related to one another than to species in
another genus because they share a
common ancestor
The higher the level of the taxon, the
further back in time the common
ancestor is to all of the organisms in the
taxon
Classification Using
Cladograms
Cladistic analysis
identifies and considers
only those characteristics
of organisms that are
evolutionary innovations
Derived characters are
characteristics that
appear in recent parts of a
lineage but not in its older
members
Classifying Using Cladograms
A cladogram is a diagram that shows
evolutionary relationships among a
group of organisms
It’s like an evolutionary family tree
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
The more similar the DNA sequences of two
species, the more recently they shared a
common ancestor, and the more closely
related they are in evolutionary terms
Molecular Clocks
A molecular clock is a model that uses DNA
comparisons to estimate the length of time that
two species have been evolving independently
Relies on mutations to mark time
The amount of differences in the DNA
sequences of two species indicates how long ago
they shared a common ancestor
Mutations that have no effect on phenotype
accumulate at a steady rate
By comparing these mutations it can be determined
how long the two species shared a common ancestor
Notes Review
Identify the purpose of cladograms
A cladogram is a diagram used to show
evolutionary relationships by using derived
characters