Phylogeny Phylogeny Evolutionary history of a species or a group of - PowerPoint PPT Presentation

Phylogeny

Phylogeny • Evolutionary history of a species or a group of species • Goal: Resulting phylogeny should match taxonomy (classification of an organism)

Phylogeny and Classification

Phylogenetic Tree • Constructed using morphological similarities (homologies) of living or fossil species, DNA and protein sequences • Show evolutionary history and relationships among groups of organisms (hypothesis) • Trees are dynamic (constantly being revised)

Understanding Phylogenies • Click on the hyperlink above for an introduction to phylogenetic trees • Read the first page and then click “next” at the bottom of the page for page 2 of Understanding Phylogenies • Write down 3 things in your notes that you learned about phylogeny by exploring this link

Tree Terminology

Tree Terminology • Sister taxa – groups of organisms that share an immediate common ancestor • Node (branch point) – represents the most recent common ancestor of a group • Root – single branch point from which all branches originate in the tree

Rooted versus Unrooted Trees

Clades • Clade: a group of organisms that consists of a common ancestor and all of its descendants

Monophyletic Group • A clade is also known as a monophyletic group

Phylogenetic Trees vs Cladograms • Sometimes used interchangeably • Branch lengths of trees may show evolutionary time and amount of genetic change

Character • Characters are heritable traits that can be compared across organisms, such as physical characteristics (morphology), genetic sequences, and behavioral traits • Example: wings shown below

Derived versus Ancestral Characters • A derived character is one that evolved in one group but not in the other group (a new trait) • An ancestral character is thought to have evolved in a common ancestor of both groups

Derived versus Ancestral Characters • Identify a derived character for mammals • Identify an ancestral character for mammals

Example of a Derived Trait • Number of heart chambers in animals • Tbx5 protein influences the formation of two ventricles in bird and mammalian hearts

Trees Show Speciation Events and Relatedness • Examine common ancestry in order to determine relatedness • Who is species 5 most closely related to?

Outgroup • An outgroup is a group of organisms that serve as a reference group when determining the evolutionary relationship among a monophyletic group of organisms • Used as a point of comparison for the ingroup • Example: - Chordates – Ingroup - Echinodermata - Outgroup

Chordate Evolution

Another Outgroup Example

Trees May Show Time and Extinct Lineages

Extinct versus Extant

Phylogenetic Trees Based on Sequence Data • Use of molecular (i.e. DNA, proteins) genetics to determine evolutionary relationships • Disadvantages – Need common genes – Gene sequences need to be “aligned” first

Sequence Alignment • Goal of Sequence Alignment: Maximize the number of matching nucleotides in all compared sequences • Compare SNPs and Indels

SNPs and Indels • SNPs – single nucleotide polymorphisms • Indels – insertions and deletions

Maximum Parsimony • Choosing a tree that requires the fewest evolutionary events (fewest amount of molecular changes) • The simplest explanation that is consistent with the facts

Which is the most parsimonious tree?

Constructing a Phylogenetic Tree • May require the use of a character table • + or 1 indicates the presence of the character, - or 0 indicates the absence of the character

Now You Try It • Based on the shared characteristics in the table below, build a tree of the most likely evolutionary history of these organisms • + (present), - (absent)