1.14 why are organisms classified into groups ?
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AIM: Why are organisms classified into groups?
Warm – up: Complete Exercise 3 in Lab
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Necessary TermsTaxonomy is the classification of organisms. Most
biologists feel that classification should be based upon phylogeny.
Phylogeny is the ancestry of organisms- how organisms are related by evolution
Systematics is the study of phylogeny.
Cladistics is a means of understanding the phylogeny of organisms.
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Phylogeny and Biochemistry
• Phylogeny of many groups has been studied by comparing structures of proteins or other biochemicals (DNA, RNA)
What about mutations?
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Molecular Clocks• Estimate time of
divergence by comparing numbers of neutral mutations in DNA, which tend to accumulate in the DNA of a lineage at a fairly constant rate.
• 70,000 years ago, Euro – Japanese split
• 140,000 African – Euro\Japanese split
• 5 mya – human – chimps split
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Biochemistry and Common Ancestry
• All use DNA (or RNA) as genetic material• All use same universal genetic code• All use same 20 amino acids in building
proteins• All use left, not right handed amino acids)
What does this information tell us?
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Cladistics and Taxonomy
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Classification in Biology
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Classification in BiologyArranging living organisms into groups
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Classification in BiologyArranging living organisms into groups
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Classification in BiologyArranging living organisms into groups
WHY BOTHER?
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Classification in BiologyArranging living organisms into groups
WHY BOTHER?1. Species Identification: Easier to find out to which
species an organism belong to if everything is organized
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Classification in BiologyArranging living organisms into groups
WHY BOTHER?1. Species Identification: Easier to find out to which
species an organism belong to if everything is organized
2. Predictive Value: If several members of a group have a particular characteristic, another species in this group may also have this characteristic
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Classification in BiologyArranging living organisms into groups
WHY BOTHER?1. Species Identification: Easier to find out to which
species an organism belong to if everything is organized
2. Predictive Value: If several members of a group have a particular characteristic, another species in this group may also have this characteristic
3. Evolutionary Links: Species in the same group probably share characterstics because they have evolved from a common ancestor
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Hierarchicalclassification
Carolus LinnaeusBinomial nomenclature
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Kingdom Phylum Class Order Family Genus Species
Seven basic categories of biological classification
More categories are added to recognize similarities among groups of taxa within these levels, for example superfamilies, etc.
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Kingdom
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Kingdom Phylum
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Kingdom Phylum Class
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Kingdom Phylum Class Order
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Kingdom Phylum Class Order Family
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Kingdom Phylum Class Order Family Genus
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Kingdom Phylum Class Order Family Genus Species
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Classification of Humans
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Kingdom (Animalia)
Classification of Humans
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Kingdom (Animalia)
Phylum (Chordata)
Classification of Humans
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Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Classification of Humans
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Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Classification of Humans
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Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)
Classification of Humans
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Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)
Genus (Homo)
Classification of Humans
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Kingdom (Animalia)
Phylum (Chordata)
Class (Mammalia)
Order (Primates)
Family (Hominidae)
Genus (Homo)
Species (Homo sapiens)
Classification of Humans
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Artificial vs. Natural Classification
• Natural Classification: matches evolutionary origins of the species in the group
• Artificial classification: Help with species identification but have no other value…
ex. Insects, birds, bats are put in the same group. WHY?
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Convergent evolution and analogous structures: Not all similarity represents common ancestry!
The Ocotillo (SW U.S.A) and Allauidia (Madagascar) are not closely related. Resemblance due to independent adaptations to similar environmental pressures.
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Organisms with homologous structures should be classified in
the same group because they have a common ancestry, even if
they look different!
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Homology vs. Analogy
• Homology refers to having a trait in common because it has been inherited from a common ancestor. – CLADOGRAMS BASED ON HOMOLOGIES
• Species can also evolve the same traits independently. Independent evolution of the same characteristic is called convergent evolution and those traits are called analagous.
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Cladograms and Classification Classification of many groups has been re-examined using
cladograms. In many cases, cladograms have confirmed existing classifications. Not surprising since both traditional classification and cladistics attempt to reflect phylogeny. Cladograms can be difficult to reconcile with traditional classifications, because the nodes can occur at any point. It can therefore seem rather arbitrary how the hierarchy of taxa is fitted to the clades. In some cases, cladistics suggests radically different phylogenies. The strength of cladistics is that the comparisons between organisms are objective, based on molecular differences. The weakness is that molecular differences are analyzed on the basis of probabilities. Occasionally, improbable events occur makine the analysis wrong. Therefore, cladistics should not be treated as infallible. However, it can stimulate a reinterpretation of the data on which traditional classifications have been based.
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Cladogram: A phylogenetic diagram that classifies organisms according to shared
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Cladogram: A phylogenetic diagram that classifies organisms according to shared
Clade: Group of organisms that evolved from a common ancestor (the ancestor plus all its descendants)
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Cladogram: A phylogenetic diagram that classifies organisms according to shared
Clade: Group of organisms that evolved from a common ancestor (the ancestor plus all its descendants)
Cladistics: method of classification of living organisms based on construction and analysis of cladograms
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Connection between classification
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Constructing a Cladogram
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Constructing a Cladogram
Ancestral (=homologous) trait: A trait shared due to common ancestry
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Constructing a Cladogram
Ancestral (=homologous) trait: A trait shared due to common ancestry
Derived trait: A trait that differs from a common ancestor
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Cats are more similar to dogs than they are to frogs, because they share a more recent common ancestor with dogs
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An outgroup is used to decide which characteristics are ancestral
Ingroup Outgroup
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Procedure 1: Classifying Doodlebirds
?
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Why are legs, beak and crest not useful in the analysis?
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(outgroup)
Web toes, Three tails
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TAXA Petal no. Leaf Seed shape
A 5 compound flat
B 4 compound round
C 4 simple round
D 5 compound round
Outgroup 4 simple round
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A B C D
A 1 (compound) 0 2 (compound, 5)
B 0 1 (compound)
C 0
D
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