Mechanisms of Evolution Flashcards
Describe how classification of organisms changed before and after Darwin
Before:
- kinds types ideals
- similarity, characteristic features
After:
- shared ancestry, phylogeny, and adaptations due to the environment
What is systematics?
- study of biological diversity
- rethinks connections between species
- studies and tries to establish PHYLOGENIES (evolutionary history)
Why might classification and phylogenies not agree?
- Linneas originally used morphological differences to categorize organisms, before evolutionary concepts arose
- So how an animal is classified, and how an animal may eventually be placed within a phylogeny/evolutionary tree, often occurs separately
What is Plesiomorphy? Symplesiomorphy?
Plesiomorphy: A ‘retained’ primitive, ancestral state or character.
Symplesiomorphy: “Together”. Shared ancestral type between multiple organisms and the ancestor
What is Apomorphy? Synapomorphy?
- Apomorphy: A new, derived trait, that has changed from the ancestor
Synapomorphy: Shared derived characters. multiple organisms who has a different trait than the ancestral
Characters vs. character states
- A character is a variable characteristic of an organism, like bill size
- a character state is the alternate conditions of a feature (Large vs small, or apomorphic vs plesiomorphic).
What is a monophyletic group?
- a set of species on a cladogram, derived from any one ancestor
- recognized by synapomorphies
- organisms with a common ancestor that are closely related
What is homology?
- Similarities due to shared ancestry
- But do NOT necessarily have the same function
- sharing of homologous features between species indicates that they have evolved from a common ancestor that possessed the same feature
- ex. tetrapods all have the same bone structure, but we all used them in different ways
What is analogy/analogous?
- similarity between structures that is not the result of a common evolutionary origin
- same function, different origin
- phenotypic similarity that gained independently and separate.
- due to convergent evolution
What is convergent evolution?
- where evolution causes species without a common ancestor to have a similar character appearance
What is parallelism?
- a subset of convergent evolution
- independent evolution of similar structures from a common ancestor
- how RECENTLY did two species have a common ancestor, where two species independently gained the same trait
What is a polyphyletic group?
a group that includes organisms with mixed evolutionary origin, and does NOT include the most recent common ancestor
- typically based on analogous characters
What is a paraphyletic group?
- group originated from a single common ancestor, but does not include all descendants from this ancestor
What is ‘branch length”
in cladograms, the length refers to the number of changes that have occurred in the branch
What is the ‘root’?
in cladograms, roots are the common ancestor of all taxa.
What is a ‘clade’?
a group of two or more taxa or DNA sequences that includes both their most recent common ancestor and all their descendants
What is ‘topology’
the branching patterns of a phylogenetic tree
What is the difference between homologies vs homoplasies?
homologies: Shared features inherited from the species common ancestor
homoplasies: shared features that are not homologies (Reversals to ancestral state or convergences)
What is the principle of parsimony?
- the simplest explanation is preferable/more likely than more complicated hypotheses that need more assumptions
How do we chose the most parsimonious tree?
- the tree with the fewest character changes.
- fewest reversals and convergences
- often the shorted trees
What are sister groups?
- monophyletic groups or individual species that are most closely related to each other
- sister group relationships are always reciprocal
What are outgroups?
- close relatives of the ingroup, used to help root the tree of the ingroup/study group
- used to indicate the direction of evolution, which character states are primitive/derived
- outgroups may represent ancestral features
what are rooted vs unrooted trees
- rooted trees present the most basal ancestor of the tree in question
- unrooted trees do not imply a known ancestral root
What are the three main strategies of rooting phylogenetic trees?
- no rooting (leaving tree unrooted, no confidence)
- mid-point rooting (rooting the tree in its middle point
- outgroup rooting ( placing the root in the right place (most confident)
