Phylogenetics Flashcards
What is the definition of phylogeny?
Evolution of a lineage into branches
What are nodes?
Points in a phylogeny where the lineage splits
What are internal nodes?
Nodes located within the phylogeny representing ancestral populations or species that have long since disappeared
What is a clade?
Single “branches” in the tree of life; each clade represents an organism and all of its elements
What does studying phylogeny allow scientists to do?
Classify species based on their evolutionary history. It gives a relative order of all the changes in lineages
What does it mean to be a monophyletic clade?
It is a group of organisms that form their own clade; an ancestor and all of its descendants
What is a polyphyletic taxon?
It is a taxon that does not include the common ancestor of all the members of the taxon
What are characters?
Heritable aspects of organisms that can be compared across taxa; can be used to determine relationships
What do the taxa that have diverged from each other more recently represent?
It represents the fact that these taxa have more character states in common than the taxa that have diverged farther in the past
What is a synapomorphy?
Derived form of a trait that is shared by a group of related species; evolved in the immediate common ancestor of a clade and were inherited by all the descendants.
AKA – changes in a character that arose in an ancestor that are
then shared by all the descendants of that common ancestor
What is the outgroup?
The species used for comparison of one group with another species outside of the clade; must have a common ancestor at some point, such as carnivores and primates
What is a homoplasy?
A character state similarity not due to shared decent, could be because of independent evolution of the same trait in two or more lineages
Define convergent evolution.
Independent origin of similar traits in separate evolutionary lineages
Define evolutionary reversal.
Reversion of a derived character state to a form resembling its ancestral state; character similarity in distantly related taxa resulting from reversal to an original state
What is a parsimony?
A principle that guides the selection of alternative hypothesis; the alternative requiring the fewest assumptions or steps is usually best
What is polytomy?
An internal node of a phylogeny with two or more branches
How do fossils help in the creation of phylogenies?
They help determine some aspects of the timing of evolution, and provide constraints to a clade’s history
Define horizontal gene transfer.
Transfer of genetic material–other than from parent to offspring–to another organism, sometimes a distantly related one, without reproduction; rather extensive amongst prokaryotes
What is exaptation?
A trait that initially carries out one function and is later co-opted for a new function; the original function may or may not be retained
How is purifying selection beneficial to a species?
It removes deleterious alleles from a population, and is a common form of stabilizing selection
What is tree thinking?
The ability to conceptualize those relationships and make inferences from the trees
What are synapomorphies important?
- used to reconstruct evolutionary trees using
one of the classic analytical methods of phylogenetics (termed cladistics) - useful for providing characters that define
parts of the Tree of Life
Every phylogeny is a ___ about the events that happened in the past
hypothesis
Why are many phylogenetic hypothesis still uncertain?
- vast number of possible topologies
2. homoplasies (convergent evolution) that obscure true relationships
What are support values on the branches?
They show how supported each branch is…usually on a 0-1 or
0-100 scale, with 1 or 100 being the most highly supported; also gives an index of how strongly that topology is
supported by the data that went into making the tree
Define an adaptation.
A trait modified by selection that increases the ability of an individual to survive or reproduce compared to individuals without the trait
What are two types of tests to study adaptation?
- experiment on variation
2. examine evolutionary history of change (comparative method)
Convergent evolution and homoplasy offer strong evidence for ___.
adaptation
What are examples of character types?
morphological, molecular, behavioral
Phylogenetic characters should be:
- heritable
- slowly-evolving
- homologous
What is a paraphyletic group?
A group with an ancestor with some, but not all, of its descendants
