Taxonomy and Classification

Introduction to Taxonomy

Taxonomy is the scientific discipline concerned with naming, describing, and classifying organisms. The modern system of taxonomy was introduced by Carl Linnaeus in the 18th century and is foundational to genetics and biology.

• Taxonomy: The science of classifying organisms based on shared characteristics.

• Classification: The arrangement of organisms into hierarchical groups.

• Binomial Nomenclature: A two-part scientific naming system for species, consisting of the genus and specific epithet (e.g., Cebuela pygmaea).

Example: The finger monkey is classified as follows:

Additional info: The binomial name is always italicized, with the genus capitalized and the specific epithet in lowercase.

Hierarchical Classification System

Organisms are classified in a hierarchy from most specific to most broad:

• Species (specific epithet)

• Genus

• Family

• Order

• Class

• Phylum

• Kingdom

• Domain

Example: Homo sapiens (humans) belong to the genus Homo, family Hominidae, order Primates, class Mammalia, phylum Chordata, kingdom Animalia, domain Eukarya.

Phylogenetic Trees and Evolutionary Relationships

Understanding Phylogenetic Trees

Phylogenetic trees are diagrams that represent evolutionary relationships among species. They are constructed using various types of data, including DNA sequences.

• Node: Represents a common ancestor.

• Branch: Represents evolutionary lineage.

• Tip: Represents a current species or taxon.

• Most Recent Common Ancestor (MRCA): The most recent individual from which all organisms in a group are directly descended.

• Sister Taxa: Two taxa that share an immediate common ancestor.

Types of Data Used: DNA, morphological traits, and other genetic evidence.

Interpreting Phylogenetic Trees

Phylogenetic trees can be used to identify evolutionary relationships, such as which species are most closely related and the sequence of evolutionary events.

• Nodes indicate speciation events.

• Branches show the passage of evolutionary time.

• Sister groups are more closely related to each other than to any other group.

Example: In a tree with species A, B, C, D, E, and F, identifying the MRCA of B and D involves finding the node where their branches meet.

Application: Finch Phylogeny

Determining Relatedness Among Finch Species

Phylogenetic trees can be used to determine which species are most closely related. For example, among finch species:

• The large cactus finch and medium ground finch are most closely related.

• The green warbler finch is least closely related to any of the others.

• The woodpecker finch is sister to the large cactus finch and medium ground finch.

• The vegetarian finch is the second oldest lineage among the five species.

Inferring Evolutionary Events

Mutations and unique traits can be mapped onto phylogenetic trees to infer when they arose in evolutionary history.

• If a mutation is present only in the vegetarian finch, it likely arose after it split from the green warbler finch and before any other evolutionary events.

• If the large cactus finch and medium ground finch share a unique trait, it likely evolved in their most recent common ancestor.

Summary Table: Key Terms in Taxonomy and Phylogenetics

Key Equations and Concepts

• Evolutionary Rate Equation:

• Cladistics Principle: Organisms are grouped by common ancestry, not just similarity.

Additional info: Phylogenetic trees are essential tools in genetics for understanding evolutionary history, speciation, and the inheritance of traits.