1. CHAPTER 26 LECTURE SLIDES
Prepared by
Brenda Leady
University of Toledo
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2. Taxonomy and systematics
Science of describing, naming, and classifying living and extinct organisms and viruses
Systematics
Study of biological diversity and the evolutionary relationships among organisms, both extinct and modern
Taxonomic groups are now based on hypotheses regarding evolutionary relationships derived from systematics

3. Taxonomy Hierarchical system involving successive levels
Each group at any level is called a taxon
Domain
Highest level
All of life belongs to one of 3 domains
Bacteria, Archaea, and Eukarya

4. Land plants and algal relatives Alveolata Stramenopila Rhizaria
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Domains:
Bacteria
Archaea
Eukarya
Eukaryotic
supergroups:
Excavata
Land plants and algal relatives
Alveolata
Stramenopila
Rhizaria
Amoebozoa
Opisthokonta
Large eukaryotic
kingdoms:
Plantae
Fungi
Animalia

5. Taxonomic group Gray wolf found in Number of species
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Taxonomic
group
Gray wolf
found in
Number of
species
Domain
Eukarya
~ 4– 10 million
Supergroup
Opisthokonta
>1 million
Kingdom
Animalia
>1 million
Phylum
Chordata
~50,000
Class
Mammalia
~5,000
Order
Carnivora
~270
Family
Canidae 34
Genus
Canis 7
Species
lupus 1

6. Binomial nomenclature
Genus name and species epithet
Genus name always capitalized
Species epithet never capitalized
Both names either italicized or underlined
Rules for naming established and regulated by international associations

7. Phylogenetic trees
Phylogeny – evolutionary history of a species or group of species
To propose a phylogeny, biologists use the tools of systematics
Trees are usually based on morphological or genetic data

8. Phylogenetic tree Diagram that describes phylogeny
A hypothesis of evolutionary relationships among various species
Based on available information
New species can be formed by
Anagenesis – single species evolves into a different species
Cladogenesis – a species diverges into 2 or more species

9. Millions of years ago (mya)
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Present B E 5 C
Time D
Millions of years ago (mya) B 10 A

11. Monophyletic group or clade
Group of species, taxon, consisting of the most recent common ancestor and all of its ancestors
Smaller and more recent clades are nested within larger clades that have older common ancestors
Paraphyletic group
Contains a common ancestor and some, but not all, of its descendents

12. H I J K L M N O H I J K L M N O H I J K L M N O D E F G D E F G D E F
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(a) Monophyletic
(b) Paraphyletic
(c) Polyphyletic

13. Reptiles were a paraphyletic groups because birds were excluded
Over time, taxonomic groups will be reorganized so only monophyletic groups are recognized
Reptiles were a paraphyletic groups because birds were excluded
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KEY
Orders
Classes
and snakes
Lizards
and snakes
Lizards
Crocodiles
Crocodiles
Turtles
Birds
Turtles
Birds
Reptiles
Reptiles
(a) Reptiles as a
paraphyletic taxon
(b) Reptiles as a
monophyletic taxon

14. Homology
Similarities among various species that occur because they are derived from a common ancestor
Bat wing, human arm and cat front leg
Genes can also be homologous if they are derived from the same ancestral gene

15. Morphological analysis
First systematic studies focused on morphological features of extinct and modern species
Convergent evolution (traits arise independently due to adaptations to similar environments) can cause problems

17. Molecular systematics
Analysis of genetic data, such as DNA and amino acid sequences, to identify and study genetic homologies and propose phylogenetic trees
DNA and amino acid sequences from closely related species are more similar to each other than to sequences from more distantly related species

18. Cladistics
Study and classification of species based on evolutionary relationships
Cladistic approach discriminates among possible phylogenetic trees by considering the various possible pathways of evolutionary changes and then choosing the tree that requires the least complex explanation for all of the available data
Phylogenetic trees or cladograms

19. Shared primitive character or symplesiomorphy
Cladistic approach compares homologous traits, also called characters, which may exist in two or more character states
Shared primitive character or symplesiomorphy
Shared by two or more different taxa and inherited from ancestors older than their last common ancestor
Shared derived character or synapomorphy
Shared by two or more species or taxa and has originated in their most recent common ancestor

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. D E F G B C A

21. Branch point – 2 species differ in shared derived characters
Ingroup – group we are interested in
Outgroup – species or group of species that is assumed to have diverged before the species in the ingroup
An outgroup will lack one or more shared derived characters that are found in the ingroup

22. (a) Characteristics among species
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Lancelet
Lamprey
Salmon
Lizard
Rabbit
Notochord
Yes
Yes
Yes
Yes
Yes
Vertebrae No
Yes
Yes
Yes
Yes
Hinged jaw No No
Yes
Yes
Yes
Tetrapod No No No
Yes
Yes
Mammary No No No No
Yes
glands
(a) Characteristics among species
Lancelet
Lamprey
Salmon
Lizard
Rabbit
Mammary
glands
Tetrapod
Hinged jaw
Vertebrae
Notochord
(b) Cladogram based on morphological traits

23. Cladogram can also be constructed with gene sequences
7 species called A-G
A mutation that changes the DNA sequence is analogous to a modification of a characteristic

25. Constructing a cladogram
Choose species
Choose characters
Determine polarity of character states
Primitive or derived?

26. Analyze cladogram based on
All species (or higher taxa) are placed on tips in the phylogenetic tree, not at branch points
Each cladogram branch point should have a list of one or more shared derived characters that are common to all species above the branch point unless the character is later modified
All shared derived characters appear together only once in a cladogram unless they arose independently during evolution more than once
Choose the most likely cladogram among possible options
Choose a noncontroversial outgroup as root

27. Principle of parsimony
Preferred hypothesis is the one that is the simplest for all the characters and their states
Challenge in a cladistic approach is to determine the correct polarity of events
It may not always be obvious which traits are primitive and came earlier and which are derived and came later in evolution
Fossils may be analyzed

28. Example 4 taxa (A-D) A is the outgroup 3 potential trees
Has all the primitive states
3 potential trees
Tree 3 requires fewest number of mutations so is the most parsimonous

29. According to the principle of parsimony, tree number 3 is the
more likely choice because it requires only five mutations.

30. Molecular clocks
Favorable mutations rare and detrimental mutations eliminated
Most mutations are neutral
If neutral mutations occur at a constant rate they can be used to measure evolutionary time
Longer periods of time since divergence allows for a greater accumulation of mutations
Not perfectly linear over long periods of time
Not all organisms evolve at the same rate
Differences in generations times

31. Evolutionary time since divergence of pairs of species
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Nucleotide
differences in
a homologous
gene between
different pairs
of species
Evolutionary time since divergence of pairs of species
(millions of years)

32. Primate evolution example
Evolutionary relationships derived by comparing DNA sequences for cytochrome oxidase subunit II
Tends to change fairly rapidly on an evolutionary timescale
3 branch points to examine (A, D, E)
Ancestor A
This ancestor diverged into two species that ultimately gave rise to siamangs and the other five species
23 million years for siamang genome to accumulate changes different from other 5 species

33. Ancestor D
This ancestor diverged into two species that eventually gave rise to humans and chimpanzees
Differences in gene sequences between humans and chimpanzees are relatively moderate
Ancestor E
This ancestor diverged into two species of chimpanzees
Two modern species of chimpanzees have fewer differences in their gene sequences

35. Ancient DNA analysis or molecular paleontology
Cooper and Colleagues Extracted DNA from Extinct Flightless Birds and Modern Species to Propose a New Phylogenetic Tree
Ancient DNA analysis or molecular paleontology
Under certain conditions DNA samples may be stable as long as 50,000 – 100,000 years
Discovery based sciences- gather data to propose a hypothesis
Sequences are very similar
New Zealand colonized twice by the ancestors of flightless birds
First by moa ancestor, then by kiwi ancestor

38. Horizontal gene transfer
Any process in which an organism incorporates genetic material from another organism without being the offspring of that organism
Vertical evolution
Changes in groups due to descent from a common ancestor

39. Due to Horizontal Gene Transfer, the Tree of Life Is Really a “Web of Life”
Vertical evolution involves changes in species due to descent from a common ancestor
Horizontal gene transfer is the transfer of genes between different species
Significant role in phylogeny of all living species
Still prevalent among prokaryotes but less common in eukaryotes
Horizontal gene transfer may have been so prevalent that the universal ancestor may have been a community of cell lineages

40. Horizontal gene transfer
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Bacteria
Archaea
Eukarya
Fungi
Animals
Plants KE Y
Vertical evolution
Horizontal gene transfer
Common ancestral community of primitive cells

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