Topic 4 Flashcards
Systematics
The theory snd practice of classifying organisms based on evolutionary history
What are phylogenies inferred from?
Morphological and molecular data
What is a phylogenetic tree?
A proposed hypothesis about evolutionary relationships among a set of organisms
What is a Basal taxon?
A group that diverges early and originates near the common ancester
Polytomy
A brance that diverges with more than two groups
What is a clade
A piece of phylogenie that includes an ancestor and all descendants
Difference between cladograms and phylograms
Cladogram - order of branching matters, evolutionary RELATIONSHIPS
Phylogram - length of branches matters, length demonstrates a timeline, evolutionary PATTERNS
When two species share a recent common ancestor, what could this indicate?
The two species are closely related
Phylogenetic trees show evolutionary ______, not progress
Relationships
Do all clades have an assigned taxonomic rank?
No
Convergent evolution
New traits form independantly due to adaptation
What trait should only be used to contruct a phylogenetic tree?
Homologous
Analogy is due to _____ evolution
Convergent
Convergent evolution
Independant evolution of similar traits in different lineages
Does convergent evolution provide information about shared evolutionary history?
No
Homoplasy
Trait shared by a set of taxa, but absent in the common ancestor
The more complex two similar structures are, the more likely that they are homologous
True
Ingroup
Group of taxa that you are interested in studying
Outgroup
One or more taxa that are related to the ingroup but diverge from the ingroup early in time
Character vs. character state
Character: anatomical, physiological, molecular features
Character state: observed prescence/absence of a character
(Some organisms have lungs, some taxa dont)
Monophyletic
A group that consists of an ancestor and all of its descendants
Cladistics
A method of inferring phylogeny from homologous traits
Paraphyletic groups
Groups with a common ancestor, but not all of their descendants are present
How do paraphyletic groups arise?
When slightly higher divergent taxa are removed from their original clade
(Any group removed = paraphyletic)
Polyphyletic group
Group that does not include the common ancestor, only includes descendants
Group is missing a common ancestor that unites the group
What is a cause of polyphyletic grouping?
Incorrect taxanomic classification
Synapomorphy
A shared derived character in a taxon shared by two or more taxa and their most recent common ancestor
But the trait is absent in the ancestor that precedes the clade
Symplesiomorphy
Shared ancestral character shared by several groups, but inherited from ancestors older than the last common ancestor
Can a characteristic be derived and ancestral in some cases?
Yes
