6.3: Classification and cladistics

Classification

involves placing organisms in groups of taxons according to their traits or evolutionary origins 

Taxons/taxa

• Any classificatory group

Taxonomy

Assigning organisms to groups

classification order…

1. Broadest: Domain

2. Kingdom

3. Phylum

4. Class

5. Order

6. Family

7. Genus

8. species

Genus

• When these diverge they can produce more genera’s 

Boundary Paradox

That speciation could occur at any moment and cannot be objectively determine forcing taxonomic rankings to be arbitrary

Classification using cell types - domains 

1. Eukaryotes

2. Prokaryotes: using ribosomal RNA they are subdivided into

   • Eubacteria

   • Archaea

Eubacteria

• walls are made up of peptidoglycan

  •  use photosynthesis

Archaea

• ell wall in archaea is made up of Pseudopeptidoglycan

  • Lacks peptidoglycan

  • Don't use photosynthesis

  • Have no nucleus

  •  adapted to extreme environments

  •  hard to culture in Laboratories so they are less research

  •  diverse energy resources used for ATP production

1. Phototrophic: Photosynthesis basically

2. Chemotrophic:  oxidizing inorganic chemicals

3. Heterotrophic: oxidation of carbon compounds from other organisms

Evolution based on evolutionary relationships

• Organisms evolved from common ancestors are put under the same taxonomic group

Synapomorphies

Shared traits within organism → allows for biologist to make classification predictions

Clades

• A group of organisms that evolved form a common shared ancestor

  • Very large groups or small

  • Includes all living and extinct species 

  • Uses base sequencing of genomes or amino acids to identify  

    • ALso uses morphological traits

• Most species are apart of many clades 

  • Smaller clades are nested in larger ones 

Parsimony Criterion

• Uses softwares to analyze the dna and its diverge

• suggests that the simplest explanation or hypothesis that fits the evidence is the most likely to be correct, requiring the fewest assumptions or changes to explain the data. 

Cladograms

• Tree with branches

• The amount of nodes they are connected by shows their relative closeness

  • More nodes = less 

• Branching tends to match phylogeny of organism 

Cladograms Terminal branches

• Ends that represent an individual clades

Cladograms Branching points/ Nodes

• Represents a common ancestor 

Cladograms root

• the base of the cladogram - hypothetical common ancestor

Cladograms Numbers

• to show sequence differences 

Cladograms Drawn to scale sometimes

•  to show time since each split 

Phylogeny

• the representation of the evolutionary history and relationships between groups of organisms

Molecular Clock

 THe method of estimating when a two species diverged from a common ancestors

• Through the accumulation of mutations in genes

• Uses the assumption that mutations accumulate at a constant rate