phylogeny and systematics chapter 26: (making “trees of life”)
TRANSCRIPT
Macroevolution•studies focus on change that occurs at or above the level of species▫The origin of taxonomic groups higher than species level
How does this occur?•Evolution of new traits (novelties)•mass extinctions•Open adaptive zones (divergent evolution)
•Currently, scientists use▫ Morphological, biochemical, and molecular comparisons to infer evolutionary relationships Obtained through fossil studies, DNA technology and current organisms
PhylogenyWhat is phylogeny?•The evolutionary history of a group
•Systematics attempts to reconstruct phylogeny, by analyzing evolutionary relatedness.▫ Use morphological and biochemical similarities
•Molecular systematics uses DNA, RNA and proteins to infer evolutionary relatedness.
•Different tools are used to reconstruct phylogenies called phylogentic trees.
Systematics•Uses evidence from fossil record and existing organisms to reconstruct phylogeny (Linneaus)
•Binomial nomenclature Genus species keeps identity of organism universal▫Other taxa used to classify
Domain, Kingdom, Phylum, Class, Order, Family, Genus, species
TaxonomyLinnaeus ordered
division of organisms into categories
based on a set of
characteristics used to assess similarities
and differences
Linking Classification and Phylogeny
•Systematists depict evolutionary relationshipsIn branching phylogenetic trees
Figure 25.9
Panthera pardus
(leopard)
Mephitis mephitis
(striped skunk)
Lutra lutra (European
otter)
Canis familiaris
(domestic dog)
Canislupus (wolf)
Panthera Mephitis Lutra Canis
Felidae Mustelidae Canidae
Carnivora
Ord
er
Fa
mil
yG
enu
sS
pe
cie
s
•“Deeper” branch points▫Represent progressively greater amounts of divergence
Leopard Domestic cat
Common ancestor
Wolf
Cladistics•Cladogram is a tree with two way branch points
•Each branch point represents divergence from common ancestor
•Each branch is called a clade
•Clades▫ Can be nested within larger clades, but not all groupings or organisms qualify as clades
•3 types of groupings ▫ Monophyletic ▫ Polyphyletic▫ Paraphyletic
Different Types of Clades•Monophyletic = single ancestor gave rise to all species in the taxon; ONLY valid clade
• Polyphyletic = includes numerous types of organisms that lack a common ancestor; not a valid clade
•Paraphyletic = a grouping that consists of an ancestral species and some, but not all, of the descendants; not a valid clade
Making “Trees”: Morphological & molecular homologies
•similarities based on shared ancestries▫bone structure ▫DNA sequences
•beware of analogous structures convergent evolution
Not all Similarities Represent Common Ancestry
•Homologous structures indicate shared common ancestry▫Homologous structures are therefore evidence of divergent evolution
•Analogous structures are similar in function but not in evolutionary history▫Analogous structures are evidence of convergent evolution
•It is not always easy to sort homologous from analogous structures
•RECALL…•Convergent evolution occurs when similar environmental pressures and natural selection▫ Produce similar (analogous) adaptations in organisms from different evolutionary lineages
Eutherian (placental)
Marsupial
•1. Cladistics = ▫sorts homologous from analogous structures▫sorts primitive and shared derived characteristics
▫Makes cladograms
Making Evolutionary Life Trees: Illustrating
Phylogeny
The Universal Tree of Life • The tree of life is divided into three great clades called domains:▫ Bacteria, Archaea, and Eukarya
Figure 25.18
Bacteria Eukarya Archaea4 Symbiosis of
chloroplast ancestor with ancestor of green plants
3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes
2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells
1 Last common ancestor of all living things
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2
3
4
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ars
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Origin of life
•A shared primitive character▫a homologous structure that is shared by all groups we are trying to define
•A shared derived character▫A new evolutionary trait unique to a particular clade(s)
▫Making Cladograms Activity Time
Phylograms• In a phylogram▫ The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage
▫ Involves timing cladograms do NOT!Dro
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