Phylogeny and the Tree of Life Quiz

Phylogeny and the Tree of Life

• Biologists estimate 5 to 100 million species of organisms live on Earth today.
• Evidence from morphology, biochemistry and gene sequences suggests all organisms are genetically related.
• Evolutionary relationships represented by a Tree of Life.
• The Tree of Life depicts the phylogeny of organisms.
• Phylogeny is the evolutionary history of a species or group.
• All life arises from a previous ancestor.
• All organisms (bacteria, fungi, protists, plants, and animals) are connected by gene passage along the phylogenetic tree.

Systematics

• Systematics classifies organisms and determines evolutionary relationships.
• Systematists use fossil, molecular, and genetic data to infer evolutionary relationships.
• Systematists depict relationships using branching phylogenetic trees.

Phylogenetic Tree

• A phylogenetic tree is a hypothesis about evolutionary relationships.
• Each branch point represents the divergence (separation) of two or more species.
• A rooted tree includes a branch to represent the last common ancestor of all taxa (group) in the tree.

Sister Taxa

• Sister taxa are groups that share an immediate common ancestor.
• In the phylogenetic tree below, domestic dog and wolf are sister taxa.

Taxon

• A taxon or taxa is a taxonomic unit (group of related organisms) at any level of hierarchy.
• Examples include Kingdom, Panthera, Felidae, Carnivora, Canis, Lutra, Mephitis.

Basal Taxon

• A basal taxon is a taxon that diverges early in the history of that group.
• A basal taxon typically originates near the common ancestor of the group.

Polytomy

• A polytomy is a branch from which more than two groups or taxa emerged.
• Polytomies represent an unknown cause of the divergence.

Phylogenetic Tree Limitations

• Phylogenetic trees show patterns of descent, not phenotypic similarity.
• Phylogenetic trees don't indicate when species evolved or how much change occurred.
• It should not be assumed that a taxon evolved from the taxon next to it.

Phylogenies from Data

• Phylogenies are inferred from morphological and molecular data.
• Organisms with similar morphologies or molecular sequences are likely more closely related.
• Phenotypic and molecular similarities are homologies that indicate a shared or common ancestry.
• The more complex two similar structures are, the more likely they are homologous.

Molecular Homology

• Molecular homology shows similarities in DNA sequence across different species.

Morphological Homology

• Morphological homology shows similarities in anatomical structures in different species.

Analogy vs Homology

• Homology is similarity due to shared ancestry.
• Analogy is similarity due to convergent evolution.

Convergent Evolution

• Convergent evolution happens when unrelated organisms face similar pressures in similar environments, leading to similar adaptations.
• Examples include wings of insects and birds, or tails of whales and fish.

Classifying Organisms

• Taxonomists classify organisms by shared characteristics or evolutionary relationships.
• Phenetic classification focuses primarily on shared traits.
• Cladistic classification focuses primarily on evolutionary relationships and shared characteristics.

Cladistics

• Cladistics aims to provide a scheme (cladogram) that shows the most likely evolutionary pathway for a species.
• A clade includes an ancestral species and all its descendants.

Monophyletic

• Monophyletic clade includes only an ancestral species and all its descendents.

Paraphyletic

• A paraphyletic group includes an ancestral species and some, but not all of its descendants

Polyphyletic

• A polyphyletic group includes various species with different ancestors.

Shared Ancestral and Derived Characters

• Organisms have shared and different characteristics compared to ancestors.
• Shared ancestral character is a character that originates in an ancestor of that taxon.
• A shared derived character is an evolutionary new trait unique to a particular clade.

Molecular Clocks

• Molecular clocks help determine how long ago two or more groups or taxa diverged from a common ancestor.
• These methods use the rate of genetic mutation in a shared ancestral gene.

From Two Kingdoms to Three Domains

• Early taxonomists classified species as either plants or animals.
• Later five kingdoms were recognized (Monera, Protista, Plantae, Fungi, Animalia).
• More recently the three-domain system was adopted (Bacteria, Archaea, Eukarya).