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INTERPRETING CLADOGRAMS BIG IDEA: PHYLOGENIES DEPICT ANCESTOR AND DESCENDENT RELATIONSHIPS AMONG ORGANISMS BASED ON HOMOLOGY THESE EVOLUTIONARY RELATIONSHIPS.

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Presentation on theme: "INTERPRETING CLADOGRAMS BIG IDEA: PHYLOGENIES DEPICT ANCESTOR AND DESCENDENT RELATIONSHIPS AMONG ORGANISMS BASED ON HOMOLOGY THESE EVOLUTIONARY RELATIONSHIPS."— Presentation transcript:

1 INTERPRETING CLADOGRAMS BIG IDEA: PHYLOGENIES DEPICT ANCESTOR AND DESCENDENT RELATIONSHIPS AMONG ORGANISMS BASED ON HOMOLOGY THESE EVOLUTIONARY RELATIONSHIPS ARE REPRESENTED BY DIAGRAMS CALLED CLADOGRAMS (BRANCHING DIAGRAMS THAT ORGANIZE RELATIONSHIPS) Interpreting Cladograms Notes

2 Reading Cladograms When an ancestral lineage splits: speciation is indicated due to the “arrival” of some new trait. Each lineage has unique traits to itself alone and traits that are shared with other lineages. each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — common ancestors. Read like a family tree: show patterns of shared ancestry between lineages.

3 Quick Question #1 What is our definition of a clade? (look back to zoology notes #1 if you cannot remember) What is our definition of a clade? (look back to zoology notes #1 if you cannot remember) A group that includes a common ancestor and all the descendants (living and extinct) of that ancestor.

4 Reading Cladogram: Identifying Clades Using a cladogram, it is easy to tell if a group of lineages forms a clade. Imagine clipping a single branch off the phylogeny  all of the organisms on that pruned branch make up a clade  So everything in the pink circle is a clade (common ancestor and all descendants)

5 Quick Question #2 Looking at the image to the right: Is the green box a clade? The blue? The pink? The orange? Looking at the image to the right: Is the green box a clade? The blue? The pink? The orange?

6 Reading Cladograms: Clades Clades are nested within one another  they form a nested hierarchy. A clade may include many thousands of species or just a few.

7 Interpreting Cladograms it's easy to misinterpret cladograms as implying that some organisms are more "advanced" than others however, cladograms don't imply this at all. when reading a cladogram, it is important to keep three things in mind

8 (mis)Interpreting Cladograms: One Evolution produces a pattern of relationships among lineages that is tree-like, not ladder-like.

9 (mis)Interpreting Cladograms: Two Just because we tend to read phylogenies from left to right, there is no correlation with level of "advancement."

10 (mis)Interpreting Cladograms: Three For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. The following phylogenies are equivalent:

11 Interpreting Phylogenies: Human Example The points described above cause the most problems when it comes to human evolution. It is important to remember that:  Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human.  Humans are not "higher" or "more evolved" than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.

12 Quick Question #3 What is this called? What do you think the red lines represent? What is this called? What do you think the red lines represent?

13 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.

14 BUT HOW DO WE CONSTRUCT A CLADOGRAM?

15 3 Alternative, mutually exclusive Cladograms How Do We Choose Between Them?

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

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

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

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

20 3 Steps 4 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?


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