BIOC51H3 Lecture : Readings 4 notes
11 Aug 2010
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Readings 4
Pgs 111-119 (refer to pgs. 366-369 and 376-379 after)
-the evolutionary history of a group of species is called its phylogeny and a phylogenetic tree is
a graphical summary of the history
-an evolutionary tree describes the pattern and timing of events that occurred as species
diversified
-synapomorphies are homologous traits that are shared among certain species and are similar
because they were modified in a common ancestor (shared derived traits)
-synapomorphies are useful in estimating phylogenies
-any group that includes an ancestor and all of its descendants is a monophyletic group
-the first idea to understanding why evolutionary relationships can be inferred by analyzing
synapomorphies is that synapomorphies identify evolutionary branch points
-the second idea is that synapomorphies are nested in that each branching event adds one or
more shared derived straits
-phylogeny inference methods that use the two ideas are called cladistic methods
-outgroup analysis is a basic cladistic method in which a relative that clearly branched off
earlier is selected as the outgroup and is compared to a group of interest
-in cases of similar traits that independently evolved in groups of species, species may share
similar traits that were not derived from a common ancestor
-morpohological similarities that have evolved independently in different lineages are due to
convergent evolution
-convergent evolution occurs when natural selection favours similar structures as solutions to
problems posed by similar environments
-evolution at the molecular level entails changes in nucleotide sequence due to mutation
-species can share nucleotide sequences for reasons other than common ancestry (caused by
reversal)
-in DNA sequence data, a change in nucleotide base is termed a reversal
-reversals are common in DNA data because there are only four possible states for each base in
a sequence
-convergence and reversal are homoplasius traits because they are not homologous
-homoplasius traits are not as similar as they initially appear because their underlying
structures are different
-morphological traits that are similar due to shared ancestry should develop in similar ways and
depend on the products of similar alleles
-homoplasius characteristics are troublesome because they suggest that two or more species
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-parsimony is a general logical criterion in which simpler explanations are preferred over more
complex ones
-when parsimony is applied to phylogeny inference, the preferred phylogenetic tree is the one
that minimizes the total amount of evolutionary change that has occurred
-it is valid to assume that convergence and reversal are rare relative to similarity
-in constructing phylogenetic trees, the goal is to measure the characteristics that are least
subject to homoplasy and the most reliable source of synapomorphies
www.notesolution.com
Document Summary
The evolutionary history of a group of species is called its phylogeny and a phylogenetic tree is a graphical summary of the history. An evolutionary tree describes the pattern and timing of events that occurred as species diversified. Synapomorphies are homologous traits that are shared among certain species and are similar because they were modified in a common ancestor (shared derived traits) Any group that includes an ancestor and all of its descendants is a monophyletic group. The first idea to understanding why evolutionary relationships can be inferred by analyzing synapomorphies is that synapomorphies identify evolutionary branch points. The second idea is that synapomorphies are nested in that each branching event adds one or more shared derived straits. Phylogeny inference methods that use the two ideas are called cladistic methods. Outgroup analysis is a basic cladistic method in which a relative that clearly branched off earlier is selected as the outgroup and is compared to a group of interest.
