Phylogeny and Systematics By: Ashley Yamachika. Biologists use systematics They use systematics as...
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Transcript of Phylogeny and Systematics By: Ashley Yamachika. Biologists use systematics They use systematics as...
Phylogeny and Systematics
By: Ashley Yamachika
Biologists use systematicsThey use systematics as an analytical approach to understanding the diversity and relationships of organisms, both present-day and extinct
Systematists use morphological, biochemical, and molecular comparisons to infer evolutionary relationships
Phylogenies are based on common ancestries inferred from fossil morphological and molecular evidence.
The Fossil RecordSedimentary Rocks…
Are the richest source of fossils
Are deposited into layers called strata
Based on the sequence in which fossils have accumulated in such strata
Fossils reveal characteristics that may have been lost over time
Radiometric Dating
Measures the decay of radioactive isotopes in terms of half-life
Half-life is the amount of time it takes for ½ the amount of a radioactive isotope to decay
Morphological and Molecular HomologiesPhylogenetic history can be inferred
from certain morphological and molecular similarities among living organisms
Organisms that share very similar morphologies or similar DNA sequences
Are likely to be more closely related than organisms with vastly different structures or sequences
Convergent Evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages
Analogous Structures or molecular sequences that evolved independently are also called homoplasies
Parallel EvolutionWhen both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not
Divergent Evolution
The diversification of an ancestral group into two or more species in different habitats is called divergent evolution.
When it involves the formation of a large number of species to occupy different niches is called an adaptive radiation.
Phylogenetic systematics connects classification with evolutionary history
TaxonomyIs the ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences.
Binomial NomenclatureIs the two-part format of the scientific name of an organism
Was developed by Carolus Linnaeus
The binomial name of an organism or scientific epithet
Is latinized
Is the genus and species
Hierarchical Classification
Systematists depict evolutionary relationships
In branching phylogenetic trees
Phylogenetic systematics informs the construction of phylogenetic trees based on shared characteristics
A cladogramIs a depiction of patterns of shared characteristics among taxa
A clade within a cladogramIs defined as a group of species that includes an ancestral species and all its descendants
CladisticsIs the study of resemblances among clades
Clades• Valid Clade is monophyletic• Signifying that it consists of the ancestor
species and all its descendants
• Paraphyletic Clade• Is a grouping that consists of an
ancestral species and some, but not all, of the descendants
PhylogramsIn a phylogram
The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage
Orthologous genesAre genes found in a single copy in the genome
Can diverge only once speciation has taken place
Paralogous genesResult from gene duplication, so they are found in more than one copy in the genome
Can diverge within the clade that carries them, often adding new functions
Neutral Theorystates that
Much evolutionary change in genes and proteins has no effect on fitness and therefore is not influenced by Darwinian selection
And that the rate of molecular change in these genes and proteins should be regular like a clock
Eubacterial• Most numerous organisms on earth • Earliest life forms (fossils date 3.5 billion years old) • Microscopic prokaryotes (no nucleus nor membrane-bound
organelles) • Have only one circular chromosome • Have small rings of DNA called plasmids • Most are unicellular
• Found in most habitats • Main decomposers of dead
organisms so recycle nutrients • Some cause disease