5.4 Cladistics Flashcards
What is cladistics?
Cladistics is a method of classifying organisms into groups of species called clades (from Greek ‘klados’ = branch)
What does each clade consist of?
Each clade consists of an ancestral organism and all of its evolutionary descendants
What will members of a clade share?
Members of a clade will possess common characteristics as a result of their shared evolutionary lineage
What is the purpose of organising clades?
Clades can be organised according to branching diagrams (cladograms) in order to show evolutionary relationships
What are cladograms and what do they represent?
Cladograms are tree diagrams where each branch point represents the splitting of two new groups from a common ancestor
What does each node represent?
Each branch point (node) represents a speciation event by which distinct species are formed via divergent evolution
What do cladograms show in terms of divergence?
Cladograms show the probable sequence of divergence and hence demonstrate the likely evolutionary history (phylogeny) of a clade
What does a fewer number of nodes show?
The fewer the number of nodes between two groups the more closely related they are expected to be
What do cladograms show in terms of evolution?
Cladograms can show evolutionary relationships and demonstrate how recently two groups shared a common ancestry
What evolutionary history do humans share with primates i.e. what common clade?
Humans, chimpanzees, gorillas, orangutans and gibbons all belong to a common clade – the Hominoids
What larger clade are hominoids a part of?
The Hominoid clade forms part of a larger clade – the Anthropoids – which includes Old World and New World monkeys
What 4 features do cladograms share?
root
nodes
outgroup
clades
What is a root on a cladogram?
Root – The initial ancestor common to all organisms within the cladogram (incoming line shows it originates from a larger clade)
What is a node on a cladogram?
Nodes – Each node corresponds to a hypothetical common ancestor that speciated to give rise to two (or more) daughter taxa
What is an outgroup on a cladogram?
Outgroup – The most distantly related species in the cladogram which functions as a point of comparison and reference group
What are clades on a cladogram?
Clades – A common ancestor and all of its descendants (i.e. a node and all of its connected branches)
Based on what two factors can cladograms be constructed?
Cladograms can be constructed based on either a comparison of morphological (structural) features or molecular evidence
Historically, structural features were used to construct cladograms, but molecular evidence is now more commonly used
How to construct a cladogram
https://ib.bioninja.com.au/standard-level/topic-5-evolution-and-biodi/54-cladistics/cladograms.html
What chemical similarity do all organisms have?
All organisms use DNA and RNA as genetic material and the genetic code by which proteins are synthesised is (almost) universal
Due to DNA almost being universal, what can be compared to ascertain evolutionary relationships?
This shared molecular heritage means that base and amino acid sequences can be compared to ascertain levels of relatedness
What will accumulate in DNA over the course of time?
Over the course of millions of years, mutations will accumulate within any given segment of DNA
What does the number of comparable base sequences demonstrate?
The number of differences between comparable base sequences demonstrates the degree of evolutionary divergence
What does a greater difference between comparable base sequences suggest?
A greater number of differences between comparable base sequences suggests more time has past since two species diverged
Therefore from base sequences, how can we determine whether organisms are evolutionarily related?
Hence, the more similar the base sequences of two species are, the more closely related the two species are expected to be