LG 4 Outline Evolutionary 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 Biology Unit III Evolution Learning 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 Characters Ancestral 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 Systematics Taxonomic Hierarchy Homoplasies Ancestral Characters Derived Characters Cladistics Cladograms Molecular Phylogenetics Molecular Clocks Analogous Structures