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Flashcards in Phylogenies Deck (30):
1

Phylogeny

the evolutionary history of a group of organisms

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Phylogenic tree

graphical summary of this history, showing the evolutionary relationships among genes, populations, species, or higher taxa

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Tree of life

the most universal of all phylogenetic trees, depicting the evolutionary relationships among all living organisms on Earth

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nodes

forks in the tree

represent hypothetical common ancestors

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Where are taxa located?

At the tips of the tree, never in the middle, even if some of the taxa are extinct

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Sister groups

share a recent common ancestor at the node where their branches meet

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What happens once species diverge?

Both species continue to evolve

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Outgroup

a taxon that diverged prior to the taxa that are the focus of the study

a sister group

helps to root the tree

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Polytomy

a node that depicts an ancestral branch dividing into 3 of more (rather than two) descendant branches

usually indicates where there was insufficient evidence to determine which taxa are more closely related

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Are the number of nodes important?

No

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Are phylogenetic trees exact?

No. They must be estimated through using a variety of data.

Phylogenetic trees are like hypotheses that can be tested and are often revised as new data becomes available

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What is the first step in inferring evolutionary relationships?

Decide which taxa to compare

Decide which characteristics to use to compare

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character or trait

any genetic, morphological, physiological, developmental, or behavioral characteristic to be studied

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Willi Henning

developed the cladistic approach

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Cladisitic approach

a way to estimate a phylogenetic tree

based on the principle that relationships among species can be reconstructed by identifying shared derived traits, called synapomorphies

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synamorphy

a trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors

can include gaining and loosing characteristics

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monophyletic group

an evolutionary unit that includes an ancestral population and all of its descendants, but no others

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paraphyletic group

a group that includes an ancestral population and some of its descendants, but not all

can be if a trait was lost in one of the descendants, not all have it

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parsimony

the most likely explanation or pattern is the one that assumes the fewest steps to reach a particular result

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In cladistics are the length of the branches important?

No

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How is parsimony implemented?

through computer programs

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homoplasy

occurs when traits are similar for reasons OTHER than common ancestry

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convergent evolution

the independent evolution of similar traits in distantly related organisms due to adaptation to similar environment and lifestyles

not due to common ancestry

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What is a cause of homoplasy?

Convergent evolution

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The whale example

Does not follow parsimony because the whale had to gain the pulley shaped astragalus and then loose it, but it is supported by fossils and DNA data

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An example of a homoplasy

Cell walls in plants and fungi

They are made out of different materials

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the best classification system...

most closely reflects evolutionary history

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molecular systematics

the use of molecular genetics to study the evolution of relationships among individuals and species

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Four chambered hearts of birds and mammals example

Their common ancestor only had a 3 chambered heart, so the four chambered heart in birds and mammals had to have evolved independently after they split from the common ancestor

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Note: figure out how to do the last problem with most parismonous tree

do practice taking data and constructing the most parismonious tree