BIO 1220 - Lecture 7

what two major analytical tools did biologists use to reconstruct the history of life?

phylogenetic trees and fossil records

define phylogeny

branching evolutionary history of a group of organisms

define a phylogenetic tree

simplified diagram of phylogeny history

what’s the most universal phylogenetic tree?

tree of life

define systematics

characterizes and classifies relationships among all organisms on earth

uses of phylogenetic trees

taxonomy, medicine, conservation

describe the different components of a phylogenetic tree

• taxa - located on the tips of branches, none are presumptive ancestors of each other

• sister groups - closely related taxa sharing recent common ancestor

• nodes - speciation events, branches can rotate at each node, not useful for determining relationships

what is a character/trait and what are the two possible states

• character/trait is any characteristic to be studied

• two possible states are present or absent

what’s an outgroup

a closely related to the study group to distinguish ancestral and derived traits, multiple outgroups used to estimate phylogenetic relationships

what’s an ancestral vs derived traits

• ancestral - character that existed in ancestor

• derived - modified form of ancestral trait found in descendant

they are relative, depending on what taxa are being compared

define synamorphies

shared derived traits present in most recent common ancestors and missing in more distant ones

what are monophyletic groups

clades/lineages, evolutionary units including ancestral species and all of its descendants

what are possible complications when inferring a tree

• similar traits due to independent evolution (homoPLASY)

• reversal in character, shows no change

• may be in group based on one trait and different in another

what are the three methods to filter probable trees and what do they do

1. parsimony:

• assumes that the most likely pattern requires the least amount of change

2. evolutionary distance:

• quantifies average frequency of character changes among pairs in taxa

• determines which tree aligns best with taxa

3. maximum likelihood and bayesian analysis:

• requires information beyond data matrix

what is convergent evolution and its relation to homoplasy

convergent evolution is where unrelated species independently evolve similar traits usually due to environmental pressures