Phylogeny and the Tree of Life Chapter 26 Phylogeny and the Tree of Life

What you need to know: The taxonomic categories and how they indicate relatedness. How systematics is used to develop phylogenetic trees. The three domains of life including their similarities and their differences.

(evolutionary history) Systematics: classifying organisms and determining their evolutionary relationships Taxonomy (classification) Systematics Phylogenetics (evolutionary history)

Tools used to determine evolutionary relationships: Fossils Morphology (homologous structures) Molecular evidence (DNA, amino acids) Who is more closely related? Animals and fungi are more closely related than either is to plants.

Taxonomy: science of classifying and naming organisms Binomial nomenclature (Genus species) Naming system developed by Carolus Linnaeus.

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Phylogenetic Tree Branching diagram that shows evolutionary history of a group of organisms

Terminology Branch Point- represents the divergence of 2 evolutionary lines Sister taxa- groups of organisms that share an immediate common ancestor (closest relative) Rooted- a branch point within the tree represents the most recent common ancestor of all taxa in tree Extant- still living Basal taxon- lineage that diverges early in history and lies on branch near common ancestor (G) Polytomy- branch point where more than 2 descendant groups emerged

3 points about Phylogenetic Trees 1) Intended to show patterns of descent not phenotypic similarities Ex) Crocodiles most closely related to birds than lizards but look more like lizards

3 points about Phylogenetic Trees 2) Sequence of branching does not always indicate absolute age of species 3) Do not assume that a taxon on a phylogenetic tree evolved from the taxon next to it

Cladogram: diagram that depicts patterns of shared characteristics among taxa Clade = group of species that includes an ancestral species + all descendents Can be nested within larger clades, but not all groupings or organisms qualify as clades Shared derived characteristics are used to construct cladograms Turtle Leopard Hair Amniotic egg Four walking legs Hinged jaws Vertebral column Salamander Tuna Lamprey Lancelet (outgroup) Cladogram

Taxon is equivalent to a clade if it is monophyletic Consists of an ancestral species and ALL its descendants

A valid clade is monophyletic Signifying that it consists of the ancestor species and all its descendants (a) Monophyletic. In this tree, grouping 1, consisting of the seven species B–H, is a monophyletic group, or clade. A mono- phyletic group is made up of an ancestral species (species B in this case) and all of its descendant species. Only monophyletic groups qualify as legitimate taxa derived from cladistics. Grouping 1 D C E G F B A J I K H Figure 25.10a

Paraphyletic Group Consists of an ancestral species and some, but not all, of its descendants

A paraphyletic clade Is a grouping that consists of an ancestral species and some, but not all, of the descendants (b) Paraphyletic. Grouping 2 does not meet the cladistic criterion: It is paraphyletic, which means that it consists of an ancestor (A in this case) and some, but not all, of that ancestor’s descendants. (Grouping 2 includes the descendants I, J, and K, but excludes B–H, which also descended from A.) D C E B G H F J I K A Grouping 2 Figure 25.10b

Polyphyletic Group Includes distantly related species but does not include their most recent common ancestor

A polyphyletic grouping Includes numerous types of organisms that lack a common ancestor Grouping 3 (c) Polyphyletic. Grouping 3 also fails the cladistic test. It is polyphyletic, which means that it lacks the common ancestor of (A) the species in the group. Further- more, a valid taxon that includes the extant species G, H, J, and K would necessarily also contain D and E, which are also descended from A. D C B E G F H A J I K Figure 25.10c

Monophyletic, paraphyletic, and polyphyletic groups

Constructing a phylogenetic tree A “0” indicates a character is absent; a “1” indicates that a character is present.

Branch lengths can represent genetic change

Branch lengths can indicate time

Draw a phylogenetic tree based on the data below Draw a phylogenetic tree based on the data below. Draw hatch marks on the tree to indicate the origin(s) of each of the 6 characters.

Answer:

Various tree layouts Circular (rooted) tree Unrooted tree Rooted tree

Principle of maximum parsimony: use simplest explanation (fewest DNA changes) for tree – “keep it simple” Occam's razor Molecular clocks: some regions of DNA appear to evolve at constant rates Estimate date of past evolutionary events Eg. Origin of HIV infection in humans= 1930’s

Tree of Life 3 Domains: Bacteria, Archaea, Eukarya

Identification of species SYSTEMATICS focuses on phylogeny Biological diversity taxonomy cladistics classification Identification of species D K P C O F G S Homologous similarities fossils binomial molecular Genus, species morphology