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Phylogeny and the Tree of Life (Shared characters are used to construct…
Phylogeny and the Tree of Life
Phylogenies show evolutionary relationships
Taxonomy is the scientific discipline that names and classifies species
In the Linnnaean taxonomic system, genera are grouped in families, which are then placed into the increasingly broader categories of orders, classes phyla, and kingdoms, and more recently into domains
A phylogenetic tree represents hypotheses about evolutionary relationships among groups
Each dichotomous branch point on a phylogenetic tree represents the divergence of two taxa from a common ancestor
A basal taxon is one that diverged early in the evolutionary history of a group
Phylogenies are inferred from morphological and molecular data
Analogy is similarity due to convergent evolution, in which unrelated species develop similar features because natural selection has led to similar adaptations
Analogous structures are also called homoplasies
Shared characters are used to construct phylogenetic trees
Cladistics bases classification on common ancestry and nests clades within clades
A clade is a monophyletic group that consists of an ancestral species and all of its descendant species
A paraphyletic group excludes some species that share a common ancestor with other species in the group, and a polyphyletic group includes several distantly related species but not their most recent common ancestor
Shared ancestral characters are found in a particular clade but originated in an ancestor that is not part of that clade
Shared derived characters are unique to a particular clade
An organism's evolutionary history is documented in its genome
Orthologous genes are homologous genes found in different species; such genes may diverge after the two species separated
Paralogous genes result from gene duplication in the same genome, and as they diverge, they provide new opportunities for evolutionary change within a species
Molecular clocks help track evolutionary time
Some regions of DNA appear to evolve at constant rates, and comparisons of the number of nucleotide substitutions in ortholgous genes can serve as molecular clocks to estimate the time since two species branched from their common ancestor
Our understanding of the tree of life continues to change based on new data
Genome comparisons from the three domains indicate that horizontal gene transfer, perhaps through exchange of transposable elements and plasmid, occurred during the early history of life