LG 4 OutlineEvolutionary Relationships and Classification

Goals of Systematics

Phylogenetic Trees –

Taxonomy –

The Linnaean System of Taxonomy

Binomial Nomenclature –

Taxonomic Hierarchy –

Traits Used in Classification

Morphological Characteristics –

Homologies –

Homoplasies (Analogies) –

Ancestral and Derived Characters –

Cladistics –

Molecular Phylogenetics –

AP BiologyUnit III

EvolutionLearning Goal 4

Describe how evolutionary relationships are used to classify

organisms.

Goals of Systematics

• Reconstruct phylogeny (evolutionary history) of a group of organisms.

This history is illustrated in phylogenetic trees.

These identify likely relationships among species.

• Taxonomy, or the identification and naming of species is the second goal.

Taxonomy also places organisms into a classification scheme.

• Naming and Classifying Organisms

• Began with the Swedish naturalist Carolus Linnaeus in the 1700’s.

The Linnaean System of Taxonomy

• He invented the system of binomial nomenclature. In this system, each species is assigned a two-part Latinized name.

• The first part identifies a group of species with similar morphology, called a genus.

• The second part is the species (specific) name.

• Linnaeus also developed a taxonomic hierarchy to arrange large numbers of organisms into more inclusive groups.

• A family is a group of genera (plural of genus) that closely resemble one another.

• Similar families are group into orders.

• Similar orders are grouped into classes.

• Similar classes are grouped into phyla (singular phylum).

• Each category of the taxonomic hierarchy is called a taxon.

• Similar phyla are grouped into kingdoms.

• All life on Earth is classified into three domains.

Traits Used In Classification

• Morphological Characteristics

Visible, measurable traits that distinguish groups of organisms from one another.

Reflect genetic differences.

Are preserved in the fossil record.

• Homologies

Similarities that result from shared ancestry.

• Homoplasies

Phenotypic similarities that evolved independently in different lineages.

Also know as analogies.

Systematists exclude homoplasies from their analyses.

• Ancestral and Derived CharactersAncestral characters are old forms of traits.Derived characters are newer forms of traits.All species exhibit a mix of both types of characters and they provide information about evolutionary relationships.

Cladistics

• A more recent approach to classification based solely on evolutionary relationships.

• Cladists group together only species that share derived characters.

• Phylogenetic trees produced by cladists are called cladograms.

Molecular Phylogenetics

• Mutations in some types of DNA appear to arise at a relatively constant rate. Differences in the DNA sequences of two species can serve as a molecular clock.

Large differences imply divergence in the distant past. Small differences suggest a more recent common ancestor.

• Since DNA provides a code for the production of proteins, these molecules can be analyzed to determine possible relationships between species.

• When two species exhibit similar amino acid sequences for the same protein, systematists infer their genetic similarity and evolutionary relationship.

Maximum Likelihood Programs

• Statistical model that constructs numerous alternative phylogenetic trees from molecular data, and estimates how likely it is that each tree represents the true evolutionary history.

• Sytematists then accept the phylogenetic tree that is most likely to be true until more data are available.

LG 4 Vocab

1. Systematics

2. Taxonomic Hierarchy

3. Homoplasies

4. Ancestral Characters

5. Derived Characters

6. Cladistics

7. Cladograms

8. Molecular Phylogenetics

9. Molecular Clocks

10. Analogous Structures