Basics, Classifications, Homology, Analogy, and Cladistics

What is phylogeny?

The evolutionary history of a species or group of related species.

What is systematics?

A discipline focused on classifying organisms and determining their evolutionary relationships.

What are systematists' main tools?

Fossils, morphological data, and molecular data (DNA, proteins).

What is taxonomy?

The science of naming and classifying organisms.

What is binomial nomenclature?

The two-part Latin name for each species (genus + specific epithet) introduced by Linnaeus.

Who developed the binomial system?

Carolus Linnaeus.

In binomial nomenclature, what part of the name is capitalized?

The genus.

In binomial nomenclature, what part of the name is lowercase?

The specific epithet (species).

How should scientific names be formatted in writing?

Genus and species should be italicized or underlined (e.g., Homo sapiens).

What is a taxon?

Any named taxonomic unit at any level of hierarchy (e.g., species, genus, family).

What is the hierarchical classification system (from broad to specific)?

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.

What mnemonic helps remember taxonomic ranks?

“Dear King Philip Came Over For Good Soup.”

What is phylogenetic classification based on?

Evolutionary relationships rather than just physical similarities.

How does phylogenetic classification differ from Linnaean classification?

Linnaean uses hierarchical ranks; phylogenetic systems reflect evolutionary branching patterns.

What is a phylogenetic tree?

A diagram that represents evolutionary relationships among organisms.

Do phylogenetic trees show phenotypic similarity?

Not necessarily — they show patterns of descent, not always physical resemblance.

What do branch points (nodes) on a phylogenetic tree represent?

The divergence of two evolutionary lineages from a common ancestor.

What is a sister taxa?

Groups that share an immediate common ancestor and are each other’s closest relatives.

What does a basal taxon represent on a phylogenetic tree?

A lineage that diverged early in the history of the group.

What is a polytomy?

A branch point where more than two lineages diverge, indicating unclear evolutionary relationships.

What is homology?

Similarity resulting from shared ancestry.

What are homologous structures?

Physical or genetic traits inherited from a common ancestor.

What is analogy?

Similarity due to convergent evolution, not shared ancestry.

What is convergent evolution?

Independent evolution of similar features in different lineages.

What causes analogous traits?

Similar environmental pressures or natural selection acting on unrelated species.

How can scientists distinguish homology from analogy?

By comparing complexity and genetic/molecular similarity — complex structures are more likely to be homologous.

What is cladistics?

A method of systematics that groups organisms by common descent.

What is a clade?

A group of species that includes an ancestral species and all of its descendants.

What makes a group monophyletic?

It contains a common ancestor and all of its descendants.

What makes a group paraphyletic?

It includes a common ancestor and some, but not all, of its descendants.

What makes a group polyphyletic?

It includes species from different ancestors (no common ancestor in the group).

Which type of grouping is used in modern classification?

Monophyletic groups, because they reflect true evolutionary relationships.

What are shared ancestral characters?

Traits that originated in an ancestor and are shared by all descendants.

What are shared derived characters?

Traits that are new or unique to a particular clade, distinguishing it from others.

What is an outgroup in cladistic analysis?

A species or group closely related to the ingroup but not part of it, used for comparison.

What is the ingroup?

The species being studied in a cladistic analysis.

How is an outgroup used to infer evolutionary relationships?

By comparing characters between the outgroup and ingroup to determine which traits are ancestral versus derived.

What is parsimony in phylogenetic analysis?

The simplest explanation with the fewest evolutionary changes is usually the most likely.

What does the principle of maximum parsimony favor?

The tree that requires the least number of character-state changes.

What is maximum likelihood in phylogenetic inference?

A method that identifies the tree most likely to produce the observed DNA data, given specific rules of evolution.