ANT333Y1 Lecture Notes - Lecture 14: Polyphyly, Autapomorphy, Paraphyly

49 views4 pages
School
Department
Course
Professor
1
ANT333 Lecture #14 Cladistics & Phylogenetic Systematics
Cladistics/Phylogenetic Systematics
Method classifies taxa into groups called clades, which consist of ancestor organism and all
descendants.
All characters shared between taxa can be divided into three types:
1. Homologies & homoplasies,
2. Shared ancestral homologies, and
3. Shared derived homologies.
Homoplasies and Homologies
Homoplasy (bad) is a convergent character - one that is shared between species but that was
not present in their common ancestor.
Homology (more helpful) is character shared between species that was also present in their
common ancestor.
Homologies
Shared ancestral homologies (symplesiomorphy - bad): found in ancestor of a group of species
but only in some of its descendants. Not what we want.
Shared derived homologies (synapomorphy - good): unique to a particular group of species (and
their ancestor). Only shared derived homologies indicate phylogenetic groups.
Cladistics/Phylogenetic Systematics
Only shared derived characters gives information about phylogeny (cladistics or phylogenetic
systematics.)
Taxa that share many derived characters are grouped more closely together than those that do
not.
Relationships are shown in branching hierarchical tree (cladogram).
Want to use as many diverse traits as possible
Cladograms
Cladogram: A branching diagram depicting hierarchical arrangement of taxa defined by
distribution of shared derived characters.
Cladogram constructed such that number of changes from one character state to next is
minimized.
Principle behind this is rule of parsimony - any hypothesis that requires fewer assumptions is a
more defensible hypothesis.
Definitions
Character: A feature or thing we can examine or label. It is important that feature be heritable.
Homologous Character: Character which is shared by taxa by descent.
Analogous Character: Shared resemblance between characters by other means than descent,
such as adaptation. This is often called a homoplastic character.
Shared Character: A character shared by all members of group
More Definitions
Unlock document

This preview shows page 1 of the document.
Unlock all 4 pages and 3 million more documents.

Already have an account? Log in

Document Summary

Ant333 lecture #14 cladistics & phylogenetic systematics. Method classifies taxa into groups called clades, which consist of ancestor organism and all descendants. All characters shared between taxa can be divided into three types: homologies & homoplasies, shared ancestral homologies, and, shared derived homologies. Homoplasy (bad) is a convergent character - one that is shared between species but that was not present in their common ancestor. Homology (more helpful) is character shared between species that was also present in their common ancestor. Shared ancestral homologies (symplesiomorphy - bad): found in ancestor of a group of species but only in some of its descendants. Shared derived homologies (synapomorphy - good): unique to a particular group of species (and their ancestor). Only shared derived characters gives information about phylogeny (cladistics or phylogenetic systematics. ) Taxa that share many derived characters are grouped more closely together than those that do not. Relationships are shown in branching hierarchical tree (cladogram).

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
Booster Classes
Class+
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
Booster Classes