Chapter 23: Understanding Diversity: Systematics

Genus

a noun and the first part of the binomial designation

Species

an adjective and the second part of the binomial designation

Ancestral Characteristics

a characteristic that is present in an ancestor and all of its descendants    

Derived Characteristics

a characteristic that appears in a recent common ancestor and is not present

earlier in that ancestral line

Clade

all the organisms in the taxa being considered together

Node

a branching point on a cladogram [a change in characteristics occurs at a node]

Root

base point and common ancestor of a cladogram

Ingroup

all the organisms in the taxa being considered together

Outgroup

a taxon that branched off before the ingroup

Mononphyletic

includes a common ancestor and all of its descendants

Paraphyletic

includes a common ancestor but not all of its descendants

Polyphyletic

a group that has evolved from more than one ancestor and does no share a common ancestor

Convergent evolution

evolution in similar environments results in similar characteristics  [e.g. flight in birds and insects]

Homologous gene

genes that are related due to sharing a common ancestor

Homologous structure         

similarities in structures due to sharing a common ancestor

Homoplasy

apparent similarity in traits due to convergent evolution or the reversal of a trait back to its ancestral state

Parsimony    

selecting the simplest explanation for interpreting taxa

Systematics

constructing cladograms [phylogenetic trees]

Phenetics [numerical taxonomy]    

uses the number of shared features to form taxa

Evolutionay taxonomy        

uses the degree of evolutionary change and phylogenetic

relationships to form taxa      

Phylgenetic systematics [cladistics]

uses most recent common ancestor and shared and

derived characteristics to form taxa

Taxonomy     

naming, describing, classifying organisms

Taxon

a formal grouping of organisms [e.g. kingdom, phylum, family, etc.]

In this figure, taxon II is

A.) monophyletic

B.) Paraphyletic

C.)Polyphyletic

D.) a clade

E.) an outgroup

B.) Paraphyletic

Explain the Movement Toward Clades (4)

-Classical phylogenetic trees have lines of unequal length that represent a period of time (branching (tree) represents hypothesized evolutionary relationships among organisms)

-All lines within a clade are equal of length (phylogenetic relationships based upon a common ancestor and its descendants)

-Classification becoming more reliant on molecular data (DNA sequences, RNA data, Protein sequencing)

-Currently a combination of classical and “modern” approaches

Explain Cladograms

a type of phylogenetic tree (forces a common ancestor as the base), but monophyletic

-represent a monophyletic clade (contains all descendants from a common ancestor)

Define Node

base of branching point

Define Root

a organism at base of cladogram under consideration (most recent common ancestor of all clades show)

Explain plesiomorphies

(shared ancestral cahracters)

-in ancestral (original) species and alll descendants (do not distinguish from another within the clade)

Ex: vertebral column in subphylum Vertebrata

Explain synapomorphies

( a “recent” development not in ancestors up to that point)

-point of divergence between groups but clade s share derived characters

Choosing taxonomic criteria (vertebrate ear bones)

-Ancestral feature: all vertebrates have ear bones

-Derived feature: reptiles have 1 but mammals have 3 (node)

Choosing Taxonomic criteria (egg laying)

-ancestral feature: birds and reptiles lay eggs

-derived feature: birds have feathers and reptiles have scales

Cladogram grouping: outgroup

taxon that branches off earlier than taxa under investigation

Cladogram groupings: ingroup

Ingroup: all taxa starting at derived character and sharing common features

Explain Monophyletic Grouping

Common ancestor and all descendants must share at least one derived character

Explain Paraphyletic grouping

Only some descendants of a common ancestor will share ancestral characters (subset of the whole)

Explain Polyphyletic grouping

Do not share common ancestor

-Unnatural grouping-misrepresents evolutionary relationships