Phylogeny Topic 7.9 Phylogeny Phylogeny is the evolutionary - - PowerPoint PPT Presentation

Phylogeny

Topic 7.9

Phylogeny

• Phylogeny is the evolutionary history of a

species or a group of species

• Goal of Phylogenetics: the resulting phylogeny

should match taxonomy (classification of an

• rganism)

Phylogeny and Classification

Phylogenetic Tree or Cladogram

• Constructed using morphological similarities

(homologies) of living or fossil species, DNA and protein sequences

• Molecular data typically provide more

accurate and reliable evidence than morphological traits

Molecular Evidence Chimpanzee is more closely related to humans than other apes Morphological Evidence (or pre-molecular data) Apes are more closely related to each other than they are to humans

Trees are Hypotheses

• Phylogenetic trees and cladograms represent

hypotheses about the evolutionary history of and relationships between groups of

• rganisms
• Trees are dynamic - constantly being revised

based on new evidence

Dinosaur Tree Revision

• Tree was revised based on research conducted
• n the hip bones of dinosaur fossils
• “Previous tree” hypothesis existed for 130

years

Understanding Phylogenies

• Click on the hyperlink above to learn about

phylogenetic trees

• Read the first page and then click “next” at

the bottom of the page for page 2 of Understanding Phylogenies

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

Phylogenetic Trees vs Cladograms

• Both diagrams show relationships between

lineages

• Phylogenetic trees show the amount of

genetic change over time calibrated by fossils

• r a molecular clock
• Cladograms do not show time

Phylogenetic Tree Cladogram

What is a clade?

• A clade is a group of organisms that consists
• f a common ancestor and all of its

descendants

Monophyletic Group

• A clade is also known as a monophyletic

group

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 shared, derived character is one that

evolved in one group but not in the other group (a new trait or evolutionary novelty)

• An ancestral character is thought to have

evolved in a common ancestor of both groups

Derived versus Ancestral Characters

• Identify a shared, 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?

Out-group

• The out-group represents the lineage that is

least closely related to the remainder of the

• rganisms in the phylogenetic tree or

cladogram

• Used as a point of comparison for the in-group

Out-group versus In-group

Phylogenetic Trees May Show Extinct Lineages

Phylogenetic Trees Show Amount of Genetic Change Over Time

Phylogenetic Trees Based on Molecular Sequence Data

• Use of molecular (i.e. DNA, amino acids)

genetics to determine evolutionary relationships

• Disadvantages?

–Need common genes between species –Gene sequences need to be “aligned” first

Sequence Alignment

(This is a tutorial on sequence alignment)

• The goal of sequence alignment is to maximize

the number of matching nucleotides in all compared sequences

• Scientists compare SNPs and Indels

SNPs and Indels

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

Maximum Parsimony

• Maximum parsimony –

the simplest explanation that is consistent with the facts

• Apply the principle of

maximum parsimony when choosing a tree as a hypothesis

• Choose the tree that

requires the fewest evolutionary events or fewest amount of molecular changes

There is a reason for this cat picture……

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, derived characters in the

table below, build a tree of the most likely evolutionary history of these organisms

• + (present), - (absent)

Stop taking notes when you get to this slide