Exam 3 Flashcards
Taxonomy
science of classifying organisms into taxa with a traditional Linnaean system (after Carl Linnaeus) uses a nested hierarchical system
At each sublevel in the taxonomic classification system, organisms become more similar.
Binomial nomenclature
Species name = genus + species ‘epithet’
Biologists group organisms based on shared characteristics. What are the 6 traits?
Fossil records
Morphology
Physiology
Behavior
Embryological development
DNA/RNA sequences
Phylogenetic systematics
Reconstruction and study of evolutionary relationships
Phylogeny
Hypothesis about relationships among taxa
Depicted as a phylogenetic tree or cladogram
A branching diagram depicting evolutionary relationships
Taxon (taxa, pl)
group(s) of organisms (species, family, domain, etc.)
Clade
any branch or lineage (lines in cladogram)
Branch point (node)
splitting represents single lineage evolving into two clades
Nodes are most recent common ancestor (MRCA) of subsequent clades
Limitations of cladograms
Often, closely related taxa look similar, but not always
If evolved under different circumstances (selection pressures), the taxa may look very different despite their close relation
Unless specified, the length of the clade does not indicate amount of time passed since divergence (node)
Two Options for Similarities
Homologous characters
Analogous characters
Analogous characters
Similar due to functional or ecological constraints/pressures
Characters can be very similar in appearance due to convergent evolution
Convergence occurs in unrelated (or distantly-related) taxa when characters are shaped by similar ecological or evolutionary constraints (selection pressures)
May be referred to as ‘homoplasy’ (instead of homology)
Homologous characters
Similar due to divergent evolution (same ancestral source)
Based on genetics and developmental origin
The deeper the similarity, the more likely it’s of same origin
Monophyletic groups (monophyly)
the most recent common ancestor and all descendants
According to cladistic analysis, only monophyletic groups should be named and recognized
Building Phylogenetic Trees
All organisms within a clade share an exclusive point (node) on the tree.
A clade may contain multiple groups, as in the case of animals, fungi and plants, or a single group, as in the case of flagellates.
Groups that diverge at a different branch point, or that do not include all groups in a single branch point, are not considered true clades.
Ancestral character state (aka plesiomorphy)
The character state present in a lineage immediately before a character state change
Found in common ancestor of taxa, but not all displayed taxa have it
Basal clade taxon is expected to display most ancestral character states
Shared derived character state (aka synapomorphy)
Arose (derived) within the larger clade
Distinguishes taxa that share it from those that do not
Provides information about relatedness within the larger group
Used to identify branch points (nodes) within the larger clade