PHYLOGENY & TAXONOMY

What is a phylogeny (evolutionary tree or cladogram)?

A diagram that shows the evolutionary relationships among species based on shared ancestry and traits.

What does each branch point (node) on a phylogeny represent?

A common ancestor shared by the descendant groups.

What does the root of a phylogenetic tree represent?

The most recent common ancestor of all organisms on the tree.

What do the tips of the branches represent?

Existing species or groups living today.

What data are used to construct phylogenies?

Morphological traits, molecular data (DNA/RNA/proteins), fossil evidence, and developmental patterns.

What is the Principle of Parsimony?

The simplest evolutionary pathway requiring the fewest changes is most likely correct.

What are shared ancestral traits?

Traits inherited from a distant ancestor that appear in multiple related groups.

Give an example of a shared ancestral trait.

The backbone shared by all vertebrates.

What are derived traits?

Newly evolved traits unique to a particular group that were not present in their ancestors.

Give an example of a derived trait.

Feathers are a derived trait unique to birds.

What is a sister taxa on a phylogeny or cladogram?

Two groups that share an immediate common ancestor; they are each other’s closest relatives.

What is an outgroup?

A species or group used for comparison that is related but not part of the studied clade.

Define taxonomy.

The scientific system of naming, describing, and classifying organisms by shared traits and evolutionary relationships.

Who developed modern taxonomy?

Carl Linnaeus.

What is binomial nomenclature?

The two-part naming system using the Genus and species (e.g., Homo sapiens).

Why are scientific names written in Latin?

Latin is universal and does not change with modern languages.

What is a taxon (plural: taxa)?

Any level of biological classification, such as species, genus, or family.

What is the Biological Hierarchical Classification System?

The system that organizes organisms into ranked groups based on shared characteristics.

List the levels of classification in order.

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

What is a mnemonic to remember the classification order?

Dear King Philip Came Over From Great Spain

What are the three Domains of life

Bacteria, Archaea, and Eukarya.

What is a clade?

A group consisting of a common ancestor and all of its descendants.

What is a monophyletic group?

A clade containing an ancestor and all its descendants.

What is a paraphyletic group?

A group that includes a common ancestor but not all of its descendants.

What is a polyphyletic group?

A group that lacks the most recent common ancestor of all its members.

What is the difference between homology and analogy?

Homology = similarity from shared ancestry; Analogy = similarity from convergent evolution.

What is convergent evolution?

When unrelated species evolve similar traits due to similar environmental pressures.

How do phylogenies help scientists?

They reveal evolutionary relationships, trace disease origins, guide conservation, and improve genetic research.

Why can phylogenies change over time?

New fossil or genetic data can reveal more accurate evolutionary relationships.

What’s the difference between a phylogenetic tree and a cladogram?

A cladogram shows relationships by traits; a phylogenetic tree may also show time or genetic distance.

What are homologous structures?

Structures that have different functions but similar forms because they come from a common ancestor.

What are analogous structures?

Structures that have similar functions but different evolutionary origins and internal anatomy.

What are vestigial structures?

Remnants of organs or structures that had a function in an ancestor but are no longer functional or necessary in the organism today.

What is divergent evolution?

When closely related species evolve different traits due to adapting to different environments.