Phylogenies & Cladograms Notes

Phylogeny

A phylogeny is a branching diagram that shows evolutionary relationships between species, usually based on DNA sequencing and other homologies.

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Cladogram

​A cladogram is similar, but shows hypothesized relationships based on shared physical homologies.

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For this class, we will treat phylogenies and cladograms as the same.

Phylogenies

The process of evolution produces a pattern of relationships between species.

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As species evolve and adaptations are inherited, their evolutionary paths split.

Phylogenies

You read a phylogeny much like you read a family tree. 

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The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendants of that ancestor.

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As you move from the root to the tips, you are moving forward in time.

Phylogenies

When a lineage splits (speciation), it is represented as branching on a phylogeny.

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When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages.

Multiple Choice

Speciation can best be defined as:

• Getting bigger, stronger, and faster over the course of a lifetime

• Descent with modification (change) from a pre-existing species

• The ability of an organism to survive, reproduce, and pass on its genes to its offspring

• The divergence (separation) of a new species from an existing species

Multiple Choice

As a species branches out and each population adapts to new locations, they eventually become so different they are now new species.

When are they no longer considered the same species?

• They can no longer breed successfully

• They do not occupy the same geographic or ecologic regions

• Their DNA and physical features differ greatly

• All of these things are used to determine species

Phylogenies

Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.​

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Phylogenies trace patterns of shared ancestry between lineages!

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Shared lineage = common ancestry!

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Multiple Choice

Species 3 is a common ancestor of which species?

• Species C only

• Species D only

• Species A and B

• Species C and D

Multiple Choice

In evolutionary terms, which species is the oldest on the phylogenetic tree?

• Species 1

• Species 2

• Species 3

• Species D

Multiple Choice

Which species is most related to Species D?

• Species A

• Species B

• Species C

• Species 1

Multiple Choice

Which species is most related to Species A?

• Species B

• Species C

• Species D

• B,C, and D are all equally related to A.

Multiple Choice

Species 2 is a common ancestor of which species?

• Species B only

• Species B and C

• Species B, C, and D

• Species A, B, C, and D

Explanations

• C and D share common ancestor 3, so they are closely related.

• A is equally related to B, C, and D. The most recent common ancestor A has with them is 1, That means species A is equally related to all the others.

• Species B, C, and D all share common ancestor 2. Species A does not.

Phylogenies

A clade is a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor. 

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Imagine clipping a single branch off the phylogeny — all of the organisms on that clipped branch make up a clade.

Multiple Choice

Which species belong in the clade for fur and mammary glands?

• Gorilla only

• Rat and gorilla

• Lizard, alligator, robin, rat, and gorilla

• Hagfish, salmon, and frog

Multiple Choice

Which species belong in the clade for claws or nails?

• Gorilla only

• Rat and gorilla

• Lizard, alligator, robin, rat, and gorilla

• Hagfish, salmon, and frog

Multiple Choice

What feature is unique to the alligator and robin?

• Feathers

• Eggs with shells

• Keratinous scales

• Claws or nails

Multiple Choice

Who is the only species that does NOT have a jaw?

• Hagfish

• Lizard

• Gorilla

• Salmon

Different styles of phylogeny / cladogram

Each of these show the same relationships between species. It is the branching pattern that is important, so the shape can vary.

Cladograms

Cladograms typically include physical features.

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These features are used to differentiate one lineage from another.

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Wherever you see a feature, all species from that point UP have the feature.

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Cladograms

As you trace a species lineage from top to base, it includes all the features on the line.

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So the rodents & rabbits have hair, amniotic eggs, four limbs, bony skeletons, and vertebrae.

Multiple Choice

What feature separates the sharks and fish from everyone else?

• Vertebrae

• Bony skeleton

• Four limbs

• Eggs with shells

Multiple Choice

What derived feature is unique to the bird and crocodile?

• Vertebrae

• Bony skeleton

• Four limbs

• Eggs with shells

Multiple Choice

What derived feature do all these organisms share?

• Vertebrae

• Bony skeleton

• Four limbs

• Eggs with shells

Multiple Choice

Which is most related to crocodiles?

• Sharks

• Birds

• Amphibians

• Primates

Multiple Choice

What features does the amphibian have?

• Vertebrae

• Vertebrae and bony skeleton

• Vertebrae, bony skeleton, and four limbs

• Vertebrae, bony skeleton, four limbs, and amniotic egg

Multiple Choice

 

According to the law of superposition, which fossil would be youngest?

• Fossil A

• Fossil B

• Fossil C

• Fossil D

Multiple Choice

Scientists can determine relatedness among organisms by comparing partial amino acid sequences. The table shows partial amino acid sequences among four organisms.

Which organism is the LEAST related to the other three organisms?

• Organism 1

• Organism 2

• Organism 3

• Organism 4