Download Classification of Living Things

Classification of
Living Things
Classification of
Living Things
Taxonomy:
Distinguishing Species
Classification of
Living Things
Distinguishing species on the basis of
structure can be difficult
Members of the same species can vary in
structure
Attempts to demonstrate reproductive
isolation is problematic because:
- Some species hybridize, and
- Reproductive isolation is difficult to observe
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Members of a Species??
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Hybridization between species
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Classification of
Living Things
What makes a species?!?
Species (def):
• a class of individuals having some common
characteristics or qualities; distinct sort or kind.
• the major subdivision of a genus of subgenus,
regarded as the basic category of biological
classification
•
composed of related individulas that resemble one
another
•
able to breed among themselves, but are not able to
breed with members of another species
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Phylogenetic Trees
Classification of
Living Things
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Systematics - the diversity of organisms at all
levels
One goal of systematics is to determine
phylogeny (evolutionary history) of a group
Phylogeny often represented as a
phylogenetic tree
A diagram indicating lines of descent
Each branching point:
- Is a divergence from a common ancestor
- Represents an organism that gives rise to two
new groups
Classification 7
and Phylogeny
Classification and Phylogeny
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Classification of
Living Things
Phylogenetic Trees
Classification lists the unique characters of
each taxon and is intended to reflect
phylogeny
Primitive characters:
- Present in all members of a group, and
- Present in the common ancestor
Derived characters:
- Present in some members of a group, but
- Absent in the common ancestor
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Classification of
Living Things
Classification and Phylogeny
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Classification of
Living Things
In terms of divergence,
which one of these is
not like the other?
Top, Middle or Bottom??
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Classification of
Living Things
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Tracing Phylogeny
Fossil Record
Fossil record is incomplete
It is often difficult to determine the phylogeny
of a fossil
Homology
Refers to features that stem from a common
ancestor
Homologous structures are related to each
other through common descent
Analogy
Similarity due to convergence
Ancestral Angiosperm
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Classification of
Living Things
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Tracing Phylogeny
Convergent Evolution
The acquisition of a feature in distantly related
lines of descent
The feature is not present in a common
ancestor
Parallel Evolution
The acquisition of a feature in two or more
related lineages
The feature is not present in a common
ancestor
Convergent Evolution
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Classification of
Living Things
Molecular Data
Protein Comparisons
Immunological techniques
- Degree of cross reaction used to judge relationship
Amino acid sequencing
- Similar sequence in same protein indicates close
relationship
RNA and DNA Comparisons
Systematics assumes:
- Two species with similar base-pair sequences are
assumed to be closely related
- Two species with differing base-pair sequences are
assumed to be only distantly related
Molecular Clocks
Use non adaptive nucleotide sequences
Assumed constant rate of mutation over time
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Ancestry of Giant Pandas??
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Molecular Data
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Classification of
Living Things
Molecular clocks provide clues to evolutionary history.
Classification of
Living Things
A quick review of gene expression
Classification of
Living Things
Classification of
Living Things
Molecular clocks use mutations to estimate
evolutionary time.
Mutations add up at a constant rate in
related species.
This rate is the ticking of the molecular
clock.
As more time passes, there will be more
mutations.
Classification of
Living Things
Molecular clocks use mutations to estimate
evolutionary time.
Mutations add up at a fairly
constant rate in the DNA of
species that evolved from a
common ancestor.
DNA sequence from a
hypothetical ancestor
Ten million years later—
one mutation in each lineage
The DNA sequences from two
descendant species show
mutations
that have accumulated (black).
Another ten million years later—
one more mutation in each lineage
The mutation rate of this
sequence equals one mutation
per ten million years.
Classification of
Living Things
Scientists estimate mutation rates by
linking molecular data and real time.
– an event known to separate species
– the first appearance of a species in fossil record
Classification of
Living Things
Mitochondrial DNA and ribosomal RNA
provide two types of molecular clocks.
• Different molecules have different mutation rates.
– higher rate, better for studying closely related
species
– lower rate, better for studying distantly related
species
• Mitochondrial DNA is used to study
closely related species.
Classification of
Living Things
– mutation rate ten times faster than nuclear DNA
– passed down unshuffled from mother to offspring
grandparents
mitochondrial
DNA
nuclear DNA
parents
Mitochondrial DNA is
passed down only from
the mother of each
generation,so it is not
subject to recombination.
child
Nuclear DNA is inherited from both
parents, making it more difficult to
trace back through generations.
Classification of
Living Things
• Ribosomal RNA is used to study distantly related
species.
– many conservative regions
– lower mutation rate than most DNA
The Three-Domain
System of Classification
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The Three Domains of Life
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