BIO topic 4: systematics and phylogenys

systematics

Discipline focused on classifying organisms based on their evolutionary relationships/ history.

phylogenetics

field of systematics focused on evolutionary relationships among organisms

phylogenetic tree

an evolutionary hypothesis of a group of relationships among organisms

depicts lineages descending from common ancestors

organize biological data

visualize evolutionary patterns

facilitate classification

how to read a Phylogenetic tree

plylograms versus cladograms

p: include measures of time, depicts hypothesis of evolutionary history, fossil is required

c: only hypothesis on the relative relationships among taxa(is A closer to B than C?)

identify clades and groups

Monophyletic: Clade that includes most recent common ancestor and all of its descendants

Paraphyletic group: a group that includes the most recent common ancestor and some of its decedents

Polyphyletic group: group that includes some of its descendants without its common ancestor

How are branches connected

Dichotomy: only two branches diverge from a common ancestor (node)

Polytomy: more than 2 branches diverge from a node

soft versus hard polytomy

s: represents uncertainty about which taxa arise from the mode are most related to each other

h: represents a hypothesis that more than 2 taxa arose from the same CA

morphological data

anatomical Features, Qual: color shape, Quant: measurements, widly used in fissils

molecular data

Genomic(DNA sequence), protein strucure, ect. organisms grouped together based on shared traits

homology

character traits that evolved from a common ancestral structure

analogy

character traits that independently evolved from convergence evolution

synapomorphy

derived feature shared by more than 2 taxa and their last common ancestor

autapomorphy

derived feature found only in ONE taxa

symplesiomorphy

ancestral feature shared by at least some members of a taxonomic group

parsimony

of all possible cladograms the one with the fewest evolutionary changes is considered the most likely(=best)

distiguishing between basal and derived character traits can be difficuls

a possible remedy: von baer’s law: the more general(basal) characteristics appear earlier in the embryo than more specialized ones.

fossil evidence: indisputable existence of a taxa in a time long past