A.P.Biology – Reading Preview: Chapter 20: Phylogeny
I.
Phylogeny: the evolutionary history of a species or group of related
species (shows evolutionary relationships)
II.
Systematics: classifies organisms and determines their evolutionary
relationships
a. phylogenetic tree represents a hypothesis about evolutionary
relationships
i. Each branch point represents the divergence of two taxa
from a common ancestor; sister taxa share immediate
common ancestor
b. Phylogenies are inferred from morphological and molecular data
III.
IV.
Taxonomy: the ordered division and naming of organisms
V.
Homology vs. analogy
a. Homology is similarity due to shared ancestry
b. Analogy is similarity due to convergent evolution
VI.
Cladistics: classifies organisms by common descent
a. A clade is a group of species that includes an ancestral species and
all its descendants
i. paraphyletic grouping: ancestral species and some, but not
all, of the descendants
ii. polyphyletic: various taxa with different ancestors
iii. An outgroup is a species or group of species that is closely
related to the ingroup, the various species being studied;
outgroup diverged before the ingroup
iv. In some trees, the length of a branch can reflect the number
of genetic changes and/or time
VII.
molecular clock: constant rates of evolution in some genes can be used
to estimate the absolute time of evolutionary change Binomial nomenclature: Linnaeus
a. two-part names for species (binomial: genus, species. First letter of
genus is capitalized, entire species name italicized)
b. hierarchical classification – grouping species in increasingly broad
categories: species, genus, family, order, class, phylum, kingdom,
and domain
a. The number of nucleotide substitutions in related genes is assumed
to be proportional to the time since they last shared a common
ancestor
VIII.
The three-domain system
a. Domains Bacteria and Archaea are single-celled prokaryotes
b. domain Eukarya: dominated bymulticellular organisms in three
lineages: kingdoms Plantae, Fungi, and Animalia
IX.
Horizontal gene transfer: there have been substantial interchanges of
genes between organisms in different domains (exchange of
transposable elements and plasmids, viral infection, and fusion of
organisms)
a. Horizontal gene transfer complicates efforts to build a phylogenetic
tree