Lecture 2 & 3 Taxonomy Flashcards
what is nomenclature?
a system of rules for naming things
what is taxonomy?
the practice of naming and classifying organisms
what is systematics?
the theory and practice of classifying organisms baed on evolutionary history (phylogeny)
what is the Linnean system?
- Carl von Linné
- use of unique binomen
- classify and group species using hierarchical categories based on relatedness and or similarity
what is the binomial nomenclature?
genus + species
what is phylogeny?
evolutionary history of a species or a group of related species
what does a phylogenic tree show?
- evolutionary relationships between organisms between common ancestors + descendants
- patterns of descent, NOT phenotypic similarity
- DONT indicate when a species evolved or how much change occurred in a lineage
- dont assume that a taxon evolved from the taxon next to it
what is a branch point/node?
divergence of 2 species, speciation event, represent common ancestors of those descendants
what are sister taxa?
two descendants that split from the same node- share an immediate common ancestor
what is a polytomy?
branch where more than 2 groups emerge
unresolved pattern of divergence
- can indicate: lack of knowledge/insufficient data to resolve
- can indicate: rapid speciation- daughter lineages are equally closely related to one another
what is a basal taxon/group?
diverges early in history originates near common ancestor of group
how are phylogenetic tree relationships interpreted?
order in which branches are split
what is an in-group?
group whose relationships we are interested in untangling
what is an out-group?
one or more taxa that are related to the ingroup, but that have diverged from it at an earlier time
what is a character & state?
character: type of structure, behaviour, DNA sequence, etc
state: manifestation of that character
what are homologies?
phenotypic and genetic similarities due to shared ancestry
- more likely with similar morphologies and DNA
- more likely with greater complexity of structure
what are homologous characters?
- look the same + have the same evolutionary origin
- usually bone structure
- phylogenetic tree building/cladistics works best when all character states are homologous
what are analogous character states?
- appear the same but actually evolved independently
- convergent evolution
- aka homoPLASIES
what is convergent evolution?
- independent evolution of similar traits in different lineages
- often similar environments + environmental pressures + NS produce similar adaptations
how is homology distinguished from analogy?
fossil evidence + degree of complexity (more complex more likely homologous)
what is cladistics?
method of inferring phylogeny from homologous characters - groups organisms by common descent
what is a valid/ideal clade?
monophyletic, ancestor species + ALL descendants, NO unrelated taxa
what is the goal of phylogenetic classification?
- organize species into groups with common ancestry that reflect ancestor-descendant relationship – ONLY MONOPHYLETIC TAXA
what is a paraphyletic grouping?
- ancestor + some but not all of descendants
- often result of removal of taxa that are HIGHLY DIVERGENT - often the group removed is monophyletic
what is a polyphyletic grouping?
- various species with different ancestors
- causes: more than one common ancestor, lacking common ancestor that unites members in a group, incorrectly grouped due to artificial similarities
what is the principle of parsimony/Occam’s Razor?
goal is to reconstruct a set of nested relationships that minimize # of times a character has to change states
- most probably phylogeny is one with the fewest evolutionary events
what is apomorphy?
derived character
what is plesiomorphy?
ancestral character
what is snapomorphy?
shared derived character
what is a symplesiomorphy?
shared ancestral character
what is an autopmorphy?
a unive derived character restricted to a single taxon
what is a phylogram?
tree where length of branch reflects # of changes that took place between taxa in that lineage
- difference between two taxa is the sum of branch lengths between common ancestor
- branch length: can be chronological time and branching points determined from fossil record or molecular clock calculations
what is the strongest support for any phylogenetic HYPOTHESIS?
- agreement bw molecular data and anatomical evidence
ultimately, what are cladograms/phylograms?
HYPOTHESES
