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What is the basis of organizing Cladograms

What is the basis of organizing Cladograms. Cladograms are built by collecting data about the characters of each organism of interest Characters are heritable traits that can be compared across organisms physical characteristics genetic sequences behavioral traits. Quick Question #1.

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What is the basis of organizing Cladograms

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  1. What is the basis of organizing Cladograms • Cladograms are built by collecting data about the characters of each organism of interest • Charactersare heritable traits that can be compared across organisms • physical characteristics • genetic sequences • behavioral traits.

  2. Quick Question #1 • Write down in your own words what some examples of characters could be. • Why are they important?

  3. Goal for making a tree The goal while making a tree is to find evidence that will help us group organisms into less and less inclusive clades. Do this by finding characters that are unique to each branching organism: derived characters

  4. Derived Characters • Shared derived characters create clades • These are our “red lines” on the cladograms we have seen. • For example: • amphibians, turtles, lizards, snakes, crocodiles, birds and mammals all have, or historically had, four limbs.

  5. Key to a good tree • Use characters that are reliable indicators of common ancestry • We use homologouscharacters • characters in different organisms that are similar because they were inherited from a common ancestor that also had that character.

  6. Quick Question #2 Not all characters are homologous even if they seem similar • Write down in your own words what homologous means • Explain you idea to the person sitting next to you.

  7. Quick Question #3 birds and bats both have wings, while mice and crocodiles do not. Does that mean that birds and bats are more closely related to one another than to mice and crocodiles? • No. When we examine bird wings and bat wings closely, we see that there are some major differences.

  8. Homologous Vs. Analogous • Bird and bat wings are analogous • Traits that have separate evolutionary origins, but are superficially similar • Evolved to serve the same function • Analogies on a cladogram:

  9. Outgroups • Another important part of creating a cladogram is the outgroup • A species/organism that is used for comparison • closely related to the groups you are creating the cladogram for • less closely related to all organisms in cladogram than any single one of the other groups is to each other. • Used to “orient” the cladogram and show an ancestral state

  10. Creation of Cladograms Given a set of observations, phylogenetic analysis seeks to find the simplest branching relationships between organisms to depict their evolution. Heritable traits possessed by organisms, characters, are used to compare the organisms being studied. • Characters can be compared across organisms • physical traits • genetic sequences • behavioral traits.

  11. BUT HOW DO WE CONSTRUCT A CLADOGRAM? ?

  12. 3 Alternative, mutually exclusive Cladograms How Do We Choose Between Them?

  13. INGROUP ORGANISMS PP RD CE Characters Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No No Yes Yes Horn No No No Yes (Not an Ancestor, but a Stand-in to represent the Ancestral Condition) Eyes Yes Yes Yes Yes Tail Yes Yes Yes Yes Mouth Yes Yes Yes Yes Outgroup Derived States Primitive (ancestral) State

  14. INGROUP ORGANISMS Outgroup PP RD CE Characters Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No No Yes Yes Horn No No No Yes Eyes Yes Yes Yes Yes Tail Yes Yes Yes Yes Mouth Yes Yes Yes Yes Derived character states found in only one organism separate them from other organisms Horn 3 Steps (evolutionary transitions from ancestral  derived) to explain this tree Wings Fur/Mane One Hoof Ancestral characters shared by all taxa link organisms together Eyes Tail Mouth

  15. Taxa Outgroup RD PP CE Characters Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No No Yes Yes Wings Loss of Wings 4 Steps (with wings developing convergently) Wings Fur/Mane One Hoof OR Wings 4 Steps (with wings developing in ancestral pony, and lost in PP)

  16. Taxa Outgroup CE PP RD Characters Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No No Yes Yes Wings Loss of Wings 4 Steps (with wings developing convergently) Wings Fur/Mane One Hoof OR Wings 4 Steps (with wings developing in ancestral pony, and lost in PP)

  17. 3 Steps The preferred cladogram is the simplest! (Least number of assumptions) So, which cladogram is the best description of the evolution of these little ponies? 4 Steps 4 Steps

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