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Biodiveristy 1: Classification
Transcript of Biodiveristy 1: Classification
Paraphyletic: Some of the descendants of 1 common ancestor.
Polyphyletic: The descendants of >1 common ancesteors.
A major goal of phylogeny is to develop a cladistic system that consists of nested monophyletic groups. ex. Homo sapiens Classification Is it a snake or a lizard? Big Questions Make Sure You Can Life's Major Divisions: Bacteria Archea Eukarya Protista Plantae Fungi Animalia Cladistics Grouping organisms according to the number of shared characteristics they have in common. This is called a "cladogram"
Can be based on any characteristics.
Ideally, it is based on "shared derived characteristics" from a common ancestor Ex. Reptiles are not a "good" phylogenetic group because they don't traditionally include birds Making a Cladogram 1. Figure out how many species have a particular characteristic in common. 2. Group species so that the most number of species have the most characteristics in common. The rule of "Maximum Parsimony":
All other things being equal*, the simplest explanation is true. Characteristics are most likely to evolve once
The rule of "Maximum Likelihood":
Assuming that mutation rates are equal in different lineages* more closely related organisms will have fewer differences in genetic sequences. Which tree is the best? Figure out shared bases Compute the possibilities, and apply maximum parsimony Ex. A phylogenetic tree that correlates DNA changes to geological time. *- these are decidedly big assumptions Old School Carl Linnaeus (1707-1778) Two contributions:
Hierarchical classification: species are grouped by similarities
Binomial nomenclature: species scientific names have two parts Genus & species: itallicized or underlined.
Genus: always capitalized
species: always lowercase Hierarchy of life: Moving from Domain to species, the number of possible groups increases.
Three domains: Bacteria, Eukarya, Archaea--based on cell anatomy.
Five (trditional) Kingdoms: Monera (bacteria), Protista, Fungi, Plantae, Animalia-- based on cell anatomy & nutritional modes. Not scientifically valid anymore.
~2 million described species: Total estimate 10-100 million. New School Some Issues With The Old Style 1. The number of kingdoms kept changing.
First two, then three, then five, then six, then eight...
2. A lot of the early work was based on visual observations.
Looks can be decieving (why?)
Described species are heavily macroscopic (why?)
99.9% of all species are microscopic. The DNA Revolution Comes to Classification DNA is a reliable indicator of relatedness.
As species diverge, their DNA sequences diverge, too.
This has revolutionized classification. Types of Groups The relationship of the 3 domains How closely related are we? DNA evidence has identified endosymbiotic ancestors What is the pattern of life's diversity that has developed during the history of life on earth?
How do we determine evolutionary relationships between organisms?
What are the characteristics of life that are useful for determining evolutionary relationships? Explain how hierarchical classification of life and binomial nomenclature work, and how they demonstrate evolutionary relationships.
Describe why classical approaches to classification have needed to be overhauled recently due to advances in molecular biology.
Explain the process of creating a cladogram and demonstrate that process if given a list of shared derived characters for a group of organisms by applying the rules of maximum parsimony and/or maximum likelihood.
Identify a taxonomic group as mono-, para-, or polyphyletic
Explain the relationship between classification and phylogeny. What Happened here? What Happened here? Placental mole Marsupial mole Phylogeny: The science of determining evolutionary relationships among organisms examples of mutations on 2 homologous DNA sequences The overall rate of mutations in genes acts as a "molecular clock" for dating evolution.
Different genes in different organisms have different mutation rates. Current phylogeny of life Gene duplications play a large role in evolution Seriously, we generally use a computer! Any Questions? Lizard! If only there were a terrible 80's rap video about the topic....