Chapter 6 - Phylogeny and Tree of Life Flashcards
Linnaean system (Linnaeus)
- Binomial nomenclature
- Hierarchical system
- Taxon
Binomial nomenclature
using 2 names to identify a particular organism
(Homo sapiens or H. sapiens)
Taxon
is a taxonomic unit at any level of the hierarchy
Classification
grouping species into broader taxonomic categories
Taxonomy
hierarchical classification, the identification, naming, and classification of species
Taxonomic Hierarchy:
Domain – Kingdom – Phylum – Class – Order – Family – Genus – Species
Systematics
the study of past and present biological diversity
But now we try to group/classify organisms based on evolutionary relationships
Phylogenies
evolutionary trees
- Hypotheses about which species are closely related and in what order they evolved
- But cannot base your hypotheses just on similarities between species:
Degree of similarity not an accurate reflection of amount of time since species diverged from a common ancestor
Convergent evolution may create similar looking species that are not closely related
Some species may evolve to look like a more distant ancestor
Node or branch point
where lineages split; the most recent common ancestor of the taxa it connects
Clade
a taxon that includes a common ancestor and ALL of its descendants. is another term for a monophyletic group.
Sister taxa
are each other’s closest relatives
Interpreting Phylogenies
To identify a taxon’s closest relative, find the closest node, and follow that branch out
Three kinds of groupings:
- Monophyletic group
- Paraphyletic group
- Polyphyletic group
Monophyletic group
common ancestor and all of its descendants (a clade) GOOD. One in which all species share a common ancestor, and the group includes all descendants of that common ancestor. Clade is another term for a monophyletic group.
Paraphyletic group
common ancestor and only some of its descendants BAD. All species share a common ancestor, but not all descendants from that common ancestor are included, e.g., class Reptilia does not include birds.
Polyphyletic group
does not include the most recent common ancestor BAD. Species that do not share a recent common ancestor are lumped together.
Constructing Phylogenies
Use CLADISTIC analysis
Objective is to determine which characteristics reveal common ancestry between two or more groups
- Emphasizes COMMON ANCESTRY as the basis of classification.
- Reflects evolutionary history
- Use of fossil record, molecular biology, morphology, comparative embryology
- Steps in creating a phylogeny:
Select the organisms to be studied
Select the characteristics to be used to separate the organisms
Select an outgroup (similar to the common ancestor)
Look at shared characteristics: used to place organisms into taxa
Shared Characteristics
ancestral (primitive)
derived
Ancestral (primitive)
(symplesiomorphies)
Traits originating in a distant ancestor and also shared by organisms outside the taxon you are studying
Derived
(synapomorphies)
Present only in the descendants of one branch of the tree (taxon) – arose within the group
Choose the best tree based on “parsimony”
- the principle that, out of all possible explanations for a phenomenon, the simplest of the set is most likely to be correct.
he simplest tree is best - i.e., the one that requires the fewest evolutionary major evolutionary events e.g., loss of a tail/evolution of fur/ etc.
Cladistics
- concentrates on order of evolution only
does not show amount of divergence over time
adjacent groups may actually be distantly related - Note that
derived characteristics may have evolved independently
derived characteristics may be lost in related groups
Homology
structures that have the same embryonic origin but may have a different function.
- E.g., parental care in birds, crocodiles, and dinosaurs = homologous
Analogy
resemblance of structures but different origin
- Saber teeth in various mammals = analogous
Exaptation
- when some biological function takes novel advantage of another function
- Features that were selected for as adaptations for one function, but that now serve a different function. (e.g., feathers and other adaptations for flight)
