Phylogenetic Trees

Phylogenetic Trees and Cladograms

• What are they? • Graphical representations (models) of

evolutionary history▫ They show how species of the past are related to

other species▫ Show relations that can be tested

• What does phylogeny mean? ▫ Phylogeny: Tracing the origin of a species based

on evolutionary relationships

Geology and the fossil record

• Fossils help us produce phylogenetictrees based on morphological characteristics

Classification of living things

• Classical taxonomy was invented by CarolusLinnaeus▫ All classification done by

physical characteristics

▫ Linnaeus invented binomial nomenclature� Two names that describe a

species� Homo sapiens

� Drosophila melanogaster

� Canis familiarus

� Mus musculus

Linnaeus• He also created hierarchical

groups of classification• Grouping organisms that seem to

be related by physical characteristics▫ Domain▫ Kingdom▫ Phylum▫ Class ▫ Order▫ Family ▫ Genus ▫ Species

Phylogenetic trees help us classify

living things

• Modern classification involves using phylogentic trees ▫ Based on evidence from

� Genetics

� Morphology

� Development

� Biochemistry

� Fossils (reveal traits that have been lost)

• The goal is to find how species are evolutionarily related▫ More in common = less likely they evolved independently

Classification and phylogeny are

linked!

• Why does classical taxonomy overlap with today’s phylogenetic trees?

• Because animals that are evolutionarily related share physical characteristics

Stop Here!

• Bring your questions for class tomorrow!

Phylogenetic trees and cladograms

• A cladogram is like a phylogenetic tree

• Both show that the relatedness of any two groups by how recently the groups have had shared a common ancestor

• How are they different? ▫ Phylogenetics is the general idea of making trees

that show evolutionary relationships▫ Cladistics creates cladograms based on shared

derived characteristics

Phylogenetic trees and cladograms• What is a shared derived

characteristic?

▫ A trait that every individual has as you move forward in the diagram

� Claws and nails are shared derived characteristics in this example for lizard, pigeon, mouse and chimp

• Example of a phylogeny

• Made with computer DNA sequencing

• Show evolutionary relationships

• Example of a cladogram

▫ Shows shared derived characteristics

� Clade: ancestral species and all of its descendants

Making a phylogenetic tree

• Based on evidence from▫ Genetics, Morphology, Development, Biochemistry, Fossils etc. ▫ Systematics: the process of analyzing this data to understand

species diversity and relationships� DNA is particularly helpful

• Morphological and molecular▫ Homology vs. analogy ▫ Divergent vs. convergent

• Molecular homologies ▫ DNA sequences▫ Proteins▫ What challenges can be anticipated with these molecules?

Making a cladogram• Look for homologous

characteristics ▫ Physical or Molecular

� DNA, Proteins

• Shared primitive characters – common to all members of the group▫ Backbone

• Shared derived characters – found only in group of interest ▫ Mammals and hair

Be careful!

• These things can make it seem like you have a relationship but they can be misleading

• Morphological homologies▫ Homology vs. analogy ▫ Divergent vs. convergent

• Molecular homologies ▫ DNA sequences▫ Proteins

Outgroup

• Species that is less closely related to the entire group, than any of the individual member are to the to other members of the group

Practice Time

• Construct a cladogram using 4 animals that you know yourself

• Include shared derived characteristics and one primitive characteristic

Practice time

• Make a cladogram with the following animals:• Identify the shared derived characteristics as well as

one shared primitive characteristic▫ Rabbit▫ Shark▫ Bird▫ Alligator▫ Chimpanzee▫ Frog▫ Trout ▫

One of many possible answers

One more

• Make a cladogram with the following animals:• Identify the shared derived characteristics as

well as one shared primitive characteristic• Identify the outgroup

▫ Rat ▫ Raccoon▫ Guinea Pig▫ Beaver ▫ Mouse ▫ Rabbit

THE NUMBER OF AMINO ACID DIFFERENCES IN CYTOCHROME c

AMONG VARIOUS ORGANISMS

28. (A) Based on the data in the table below, draw a phylogenetic tree that reflects the evolutionary relationships of the organisms based on the differences in their cytochrome c amino-acid sequences. Based on the data, identify which organism is most closely related to the chicken and explain your choice.

Horse Donkey Chicken Penguin Snake

Horse 0 1 11 13 21

Donkey 0 10 12 20

Chicken 0 3 18

Penguin 0 17

Snake 0

Cladograms and phylogenetic trees are

a work in progress• Constantly being revised based on new data

• Scientists like to fight