BLG 144 Lecture Notes - Lecture 9: Phenetics, Synapomorphy, Chapter 27
27 Apr 2018
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CHAPTER 27 PHYLOGENIES AND THE HISTORY OF LIFE
Phylogenetic trees – document evolutionary relationships among organisms and are estimated from
data
Fossil record – give physical evidence of organisms that lived in the past
Mass extinctions – happened throughout history of life. When environmental catastrophes that rapidly
eliminate most of the species alive
Two major analytical tools that biologists use to reconstruct the history of life : phylogenetic trees and
fossil records
Studying history: Phylogenetic trees
Phylogeny
- evolutionary history of a group of organisms
- summarized in phylogenetic trees that show ancestor- descendant relationships among populations or
species
Reading phylogenetic tree
- Branch – population through time
- Node ( fork) – point where branches diverge, shows point in time when an ancestor splits into 2
or
more descendent species
- Tip (terminal node) – endpoint of a branch, shows a group(spcies or larger taxon) that is living or
extinct
Estimating Phylogenies
- Researchers analyze morphological and/or genetic characteristics to get phylogenetic
relationships among species
- 2 general strategies:
- Phenetic approach – phylogenetic tree is based on computing a statistic that
summarizes the overall similarities amongst different populations.
- Cladistic approach - phylogenetic tree is based on synapomorphies (shared derived
characters of the species under study
▪ Synapomorphies allow biologists to see monophyletic groups (clades or
lineages) that are shared cause of common ancestor
Ancestral trait – characteristic that existed from an ancestor
Derived trait – modified form of ancestral trait in a descendant
Problem with phenetic and cladistic analyses - Similar Traits can evolve independently in two distant
species rather than a trait from its common ancestor
Homology – when traits are similar due to shared ancestry
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 27 phylogenies and the history of life. Phylogenetic trees document evolutionary relationships among organisms and are estimated from data. Fossil record give physical evidence of organisms that lived in the past. Mass extinctions happened throughout history of life. When environmental catastrophes that rapidly eliminate most of the species alive. Two major analytical tools that biologists use to reconstruct the history of life : phylogenetic trees and fossil records. Evolutionary history of a group of organisms. Summarized in phylogenetic trees that show ancestor- descendant relationships among populations or species. Node ( fork) point where branches diverge, shows point in time when an ancestor splits into 2 or more descendent species. Tip (terminal node) endpoint of a branch, shows a group(spcies or larger taxon) that is living or extinct. Researchers analyze morphological and/or genetic characteristics to get phylogenetic relationships among species. Phenetic approach phylogenetic tree is based on computing a statistic that summarizes the overall similarities amongst different populations.
