Lecture 4 Flashcards
Taxonomy
Study organisms, name them and put them into groups of related organisms
- Nomenclature: Organizing the naming scheme
- Classification: Putting organisms into similar groups
Phlyogeny
Deduce evolutionary relationships between organisms based on their classification
Cladistics
An approach for systematics saying that organisms should be classified using ancestral relationship as the primary criteria
Why is cheetah a cat then if it has claw trait related to other carnivores
According to cladistics, cheetah’s share common ancestry with other cats - classification is based on many traits not just a specific anatomy
Phylogenetic tree
Branched tree like representation of the relationships of organisms
- Hypothesis of the evolutionary relationship of organisms
Relationship is not concrete: Classification may change depending on what trait you prioritize
Basic features of a phylogenetic tree
Branch point: A common ancestor diverges into different species at the branch point
Dichotomy: A branch point where the common ancestor diverges into exactly two lineages
Root: The branch which represents the common ancestor of all taxa in tree
Sister taxa: Group of organisms that share an immediate common ancestor that is not shared by any other group
Sister taxa is a relative concept based on which
Common ancestor you chose to group the organisms
Basal taxon
Lineage that diverges from all the other members of the tree early in the history of the group
- Also called basal group
Properties of a phylogenetic tree
Property 1: Only shows how each organisms are connected to one another (only information contained unless otherwise noted)
- Phylogenetic trees can be drawn in different shapes without changing the meaning
Property 2: Tree shows patterns of descent. This may not always correspond to how similar organisms look or behave
Property 3: Tree does not infer that a taxon evolved from a neighbouring taxon
ex: Tree does not state that humans evolved from chimps but states that they had a common ancestor
Basic phylogenetic trees: Cladograms
A basic tree only shows how each organisms are connected to one another unless stated otherwise
Basic phylogenetic tree: Phylograms
Trees where additional information is represented typically by lengths of each branch. Branch length may correspond to the amount of genetic change, amount of time
How is speciation believed to occur
Dichotomy: A branch point where the common ancestor diverges into exactly 2 lineages
A perfect tree will have all species resolved by dichotomies but in some cases, not enough data is available to do so
Polytomy
A speciation event showing a common ancestor diverging into more than two species at once
