16. Tree of Life

All life share a single-clled answer that live around….

3-4 billion years

Phylogenis show eveoulinatry relatiohsips

• A phulogenti tree is a branching diagram that represtns a hyphteis sabout the eveouitonatry shitory of a gorup of organisms

• root rperesnts the acncestral lineage

• the branch tips rpresnt the most recent decdeants of that ancestory

• move from root ot tips, move forwards in time

phyogneies part 2

• evolutionary lineage is a sequence of ancestrao organizsm leading to desednace taxon

• branch point (node) represtn common answector (speciation) for two speices

• most resent coone ancestor (MRCA) of a group is the toungest reatlive from which all te lineages in the grup are direclty descended

Phlogentic tree groups

• Monophletic group: consits of an ancestral speices and all of its descendants

• Paraphyletic Group

• Consits of an ancersta speices and some not all of its decdentas

• Polypheltic group

• Incoudles dsitna ce relates pecies but not MRCA

Sister taxa

groups that share a common ancestor

Phylogenies are used to classify organims

• Systmatics is a displine focused on calssifying thier evoulitnary relationships

• systeamtis ahve porposed that classification be based on eveonianry relationshipis (doesnt’ always match the classic classifcations)

Phylogenies are inferred from morphological and molecular data

• systematits use data on the morhopolgy, physiology, and genes of organims to inger phylogeny

• Organims with simil phetypes or DNA sequence are more closley related than those that vastly differn in sturcutre and sequence

• Idnetification of the clades in which shared derived characters first apperad can be used to inger eveoularny realtionships

Organims share characters with thier ancestors but also have uniqe characters

• shared ancestral character is a character that orgniated in an ancesotr of the taxon

• A derived charafter is an eveoulantry novelty unqie to a particula cade

• Character are rperseted as has marks on phylgentic trees

Not all morphological similarty is proportional to realtedness

• in some cases morpholfical divergence cna be great between speices that are genetical similar, sea cucmbers are gentically similar to sea stars, brittle stars, etc.

• Unlreated species evolve superfical similarites through convergen eveoultion in response to natrual selection to similar enviromental condtions

Homology

share ancestery

anaogly

convergent eveoultion s

outgroup

a speices or group of speices closely realted to but not part of the group of speices being studies (ingroup)

using shared derived characters to inger phylogeny

• characters shared by the outgroup and ingorup ar eassumed to be ancestral

• Each group derived character is assumed to have arisen only once in the group

• the point at which charaters were derived can be the determiend by comparing members of the ingroup with each other and the outgroup

Brnahc lengths in phylogentic tress

• be arbitatry: all place in line no time sclae

• Reporesnt time: all extant taza are in line with brnahc points at correct time

• Represnt genetic divergence: branch length is proportional to the number of genetic changes that have etake place in the Dna sequence in that lineage

Methods to detmerne the best tree

• Maximum parismony assumes that the most likely tre is the one the requiers the fewest eveoulatnry events (apperances of shared derived characters)

• in phylogenis based on DNA, the most parismouns ree has the fewest base changes