phylogenetic trees

lect. 15, bio 121

phylogenetic tree

diagram that depicts the hypothesized evolutionary relationships amongst other species/taxa

cannot know evolutionary relationships with absolute certainty

why are phylogenetic trees hypothesized?

polytomy

3 or more branches in one node of phylogenetic tree

tip of branch

taxon- represent species, youngest lineage

extant

opposite of extinct

root

represents the oldest lineage on the phylogenetic tree

inferred speciation event

represented by branching points on phylogenetic tree- where ancestral population splits into 2 descendant lineages

node

last common ancestor of the 2(+) lineages descended from that node

tree topology

summary of relationships of all the taxa

character states

marks placed on trees to show when a new character state arose/lost in lineage

all descendants inherited trait unless tree indicates otherwise

what should we assume when character state appears?

monophyletic groups (clades)

group/collection of organisms that include most CA of all organisms and all descendants of that CA

sister taxa/group

2 descendants that split from the same node, each other’s closest relatives

group does not contain all descendants from CA/group does not contain CA

when is a group not monophyletic?

paraphyletic group

group that contains the CA but not all descendants

polyphyletic group

group that does not include the CA

synapomorphies

homologous traits that were inherited from the most recent CA to the group

behavioural, structural, molecular homologies

types of synapomorphies

characterizes monophyletic traits

what do synapomorphies do?

symplesiomorphy

homologous trait inherited from a more distant ancestor

DNA in cats and humans are homologous but not inherited from most recent CA

example of symplesiomorphy

autapomorphy

trait unique to one lineage

parsimonious

fewest number of changes required

parsimony

assumption that the simplest explanation is most likely to be true- used to determine which tree prepresents the “best hypothesis”

arise due to convergent evolution

analogous traits or homoplasies…

convergent evolution

independent solution to an environment demand, not from CA