Cladograms and Phylogenetic Trees 2.29.18 PM PDF

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Summary

Marios Papagapiou taught this class and had a variety of notes and presentation that walks through grade 11 biology quite well. This will help any students that need to get good grades in biology....

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M. Papagapiou – SBI3U1: Grade 11 University Biology Preparation DIVERSITY – Cladograms and Phylogeny Semester: _______, Month: _______, Year: _______

A cladogram (from Greek clados "branch" and gramma "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to descendants, nor does it show how much they have changed, so many differing evolutionary trees can be consistent with the same cladogram. A cladogram uses lines that branch off in different directions ending at a clade, a group of organisms with a last common ancestor. There are many shapes of cladograms, but they all have lines that branch off from other lines. The lines can be traced back to where they branch off. These

branching

off

points

represent a hypothetical ancestor (not an actual entity) which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of various features, adaptation, and other evolutionary narratives about ancestors. Now we can ask the question what phylogeny is and move on to the topic oh phylogenetics. A phylogeny is a is a description of the evolutionary history of relationships among organisms (or their parts). A phylogenetic tree is a diagram that portrays a reconstruction of that history. Phylogenetic trees are commonly used to depict the evolutionary history of species, populations, and genes . Each split (node) in a phylogenetic tree represents a point at which lineages diverged in the past. In the case of a species, these nodes represent past speciation events, when one lineage split into two. Thus, a phylogenetic tree can be used to trace the evolutionary relationships

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M. Papagapiou – SBI3U1: Grade 11 University Biology Preparation DIVERSITY – Cladograms and Phylogeny Semester: _______, Month: _______, Year: _______

from the ancient common ancestor of a group of species, through the various speciation events when lineages split, up to the present population of organisms. ALL OF LIFE IS CONNECTED THROUGH EVOLUTIONARY HISTORY! Phylogenies are constructed from many sources of data. (I)

Morphology:

The presence, size, shape, and other attributes of body parts. (II)

Development:

Observations of similarities in development patterns may also reveal evolutionary relationships. (III) Paleontology: The fossil record is another important source of information on evolutionary history. Fossils show us where and when organisms lived in the past and give us an idea of what they looked like. Fossils provide important evidence that helps us distinguish ancestral from derived traits. The fossil record can also reveal when lineages diverged and began their independent evolutionary histories. (IV) Behaviour: Frogs calls for example are genetically determined and appear to be acceptable sources of information for reconstructing phylogenies. (V)

Molecular data:

All heritable variation is encoded in DNA, and so the complete genome of an organism contains an enormous set of traits. In recent years DNA sequences have become one of the most widely used sources for constructing phylogenetic trees.

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M. Papagapiou – SBI3U1: Grade 11 University Biology Preparation DIVERSITY – Cladograms and Phylogeny Semester: _______, Month: _______, Year: _______

Food for thought: Although the construction of phylogenetic tree is conceptually straightforward, the computations involved with large sets of traits and taxa can be challenging. For perspective, the number of possible phylogenetic trees for just 50 species greatly exceeds the number of atoms in the universe – obviously, some serious computing power is required! Take a closer look at the cladogram on page one and compare it to the phylogenetic tree above and some of the salient differences would be obvious.

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M. Papagapiou – SBI3U1: Grade 11 University Biology Preparation DIVERSITY – Cladograms and Phylogeny Semester: _______, Month: _______, Year: _______

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M. Papagapiou – SBI3U1: Grade 11 University Biology Preparation DIVERSITY – Cladograms and Phylogeny Semester: _______, Month: _______, Year: _______

Just for your interest!

A current Phylogenetic Tree of Homo sapience and our close extinct relatives.

At times in the past, more than one species of hominid lived on Earth at the same time. Originating in Africa, hominids spread to Europe, Asia; modern Homo sapience has colonized nearly every corner of the planet.

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