Understanding Diversity: Phylogeny and Taxonomy, Slides of Biology of microorganisms

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DIVERSITY of LIFE

S3512ED/BLG 3512

Semester 2, 2023 UNIT 1: UNDERSTANDING DIVERSITY

Learning Objectives:

• Explain the concept of Phylogeny and
• Interpret phylogenetic trees, including all associated terms and branch lengths.
• Explain the concepts of taxonomy and binomial nomenclature
• Discuss Hierarchical classification in view of phylogenetic classification systems
• Explain the link between phylogeny and classification
• Deliberate on the applications of phylogeny and it’s importance
• Combine the morphological and molecular homologies and the concept of Cladistics
• Distinguish between rRNA and mtDNA as well as orthologous and paralogous genes
• Explain Maximum Parsimony vs Maximum Likelihood

 FOSSIL RECORD Petrified forest (stone forest): Accumulation of enormous fossilized tree trunks about 280 million years old.  Trunks haven’t grown in today’s Namibia but were washed down a river in ancient times when one of the many Ice Ages ended on the Gondwana continent.

Phylogeny and the Tree of Life

 A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa.  The tips of the tree represent groups of descendent taxa (often species) and the nodes on the tree represent the common ancestors of those descendants.

Phylogenies show evolutionary

relationships

 Taxonomy is the ordered division and naming of organisms In the 18th century, Carolus Linnaeus published a system of taxonomy based on resemblances Two key features of his system remain useful today: two-part names for species and hierarchical classification

Binomial Nomenclature

The two-part scientific name of a species is called a binomial The first part of the name is the genus The second part, called the specific epithet, is unique for each species within the genus The first letter of the genus is capitalized, and the entire species name is italicized  Underline separately when handwritten Both parts together name the species (not the specific epithet alone)

Hierarchical Classification

 Linnaeus introduced a system for grouping species in increasingly broad categories  The taxonomic groups from broad to narrow are domain , kingdom , phylum , class , order , family , genus , and species  A taxonomic unit at any level of hierarchy is called a taxon

Species: Panthera pardus Genus: Panthera Family: Felidae Order: Carnivora Class: Mammalia Phylum: Chordata Kingdom: Animalia Bacteria Domain: Eukarya Archaea

Linnaean classification and phylogeny can differ from each other Systematists have proposed the PhyloCode , which recognizes only groups that include a common ancestor and all its descendents A phylogenetic tree represents a hypothesis about evolutionary relationships Each branch point (node) represents the divergence of two species  Sister taxa are groups that share an immediate common ancestor

 A rooted tree includes a branch to represent the last common ancestor of all taxa in the tree  A polytomy is a branch from which more than two groups emerge

What we CAN and Cannot Learn

from Phylogenetic Trees

Phylogenetic trees DO show patterns of

descent

Phylogenetic trees DO NOT indicate WHEN

species evolved or how much genetic

change occurred in a lineage

It shouldn’t be assumed that a taxon evolved

from the taxon next to it

Only infer that they evolved from a common ancestor

Phylogeny in Court: Forensic

Science

Phylogenies are inferred from

morphological and molecular data

 To infer phylogenies, systematists gather information about morphologies, genes, and biochemistry of relevant organisms  Organisms with similar morphologies or DNA sequences are likely to be more closely related than organisms with different structures or sequences  When constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy  Homology is similarity due to shared ancestry  Analogy is similarity due to convergent evolution