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Transcript of Phylogenetic Trees - BEHS SciencePhylogeny: Tracing the origin of a species based on evolutionary...
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