BIOL165 Study Guide - Midterm Guide: 18S Ribosomal Rna, 16S Ribosomal Rna, Symplesiomorphy

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5 Aug 2016
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Biology 165: Diversity of Life
Midterm 1 Review
The Earth is 4.5 billion years old
oCellular life began 4 billion years ago
oModern humans appeared about 150,000 years ago(0.00015 bya)
Geologic time scale: based on fossil, geologic, and other types of data
Big 5 Extinction events (Phanerozoic):
oP/T (Permian/Triassic): 96% species extinct 250 mya  most severe extinction event
oK/T (K/P): 55 million years ago  loss of dinosaurs
o Triassic/Jurassic: 200 million years ago
oDevonian/Carboniferous: 375 million years ago
oOrdovician/Silurian: 450 million years ago
Hypothesis on the Origin of Life on Earth
3.5 bya prokaryotes evolved; life must have evolved surprisingly quickly once conditions
permitted
The RNA world: Thomas Cech discovered RNA that catalyzes its own excision (self-splicing RNA)
– replication (ciliates)
oHe also discovered that RNA is a coding molecule that is later on replaced by DNA
oIt was a big step to evolve a lipoprotein membrane to enclose the RNA for protection
Origins of Free Oxygen on Earth
Primary atmosphere: mainly H2 and He  was lost very early
Secondary atmosphere: developed from volcanic gases
oWas a reducing atmosphere where chemotrophs and anaerobes dominated
After photosynthetic cyanobacteria evolved, the O2 amount slowly increased
About 2 bya, the atmosphere became oxygenating allowing for aerobes to become dominant
oEvolution of metazoans, fungi, and plants was possible
There are about 1.7 million species discovered
oInsects: 1 million  best studied and very diverse
oInsects and flowering plants make up majority of known species
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Variation in Sizes of Cells
The largest cell can be several cm and house several nuclei
oAceabularia Chlorophyta
Some can reach meters in length (nerve cells can be longer)
oCaulerpa Chlorophyta
Bacteria are close to the size of a nucleus; viruses are much smaller
Cyanobacteria (blue/green algae) can be as large as eukaryotic cells
In the last 0.2 billion years, organisms (like dinosaurs) became large
Redwood tree: tallest at 115 m
Sequoia tree: widest and biggest girth, 84 m
The blue whale is currently the largest animal at 30 m
Variation in the Amount of DNA/Cell
Whisk fern (Psilotum) has the largest amount of DNA
Large amounts of DNA = numerous chromosome copies = polyploids
Less than 1% of DNA is transcribed to make the organism – nearly all DNA is not transcribed
Complexity is not tied to the amount of DNA present
Constructing vs Teaching Classification Systems
Built from the bottom up
oAt the highest level, divisions and phyla (same thing) are grouped into kingdoms and
share basic characteristics
The 3 very broad domains (eukaryotes, prokaryotes; archaea and bacteria) are not part of the
codes (the book of rules for naming species of plants)
Taught from the top down
Examples are presented at genus level only
Cyptic: organisms that cannot be morphologically distinguished and thus gene sequencing must
be done
Rules of Nomenclature
1. Bacteriological code: bacteria and archaeons
2. Zoological code: some protistans and animals
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3. Botanical code: fungi (protoctistans and eumycotan), algae (protoctistans), and plants
The Barcode works on animals by use of genes, but not on plants – botanists are independent
Biocode: a set of rules for all organisms
oFailed because scientists could never reach an agreement
Phylocode: constantly expanding data on DNA based on phylogenies
Bacteriological code: uses rRNA sequencing
oBacteria: 16s rRNA gene is useful for nomenclature because it is found in all species in
the domains  not often laterally transferred
oEukaryotes: 18s rRNA (homologous to the 16s rRNA gene – same evolutionary history;
share a common ancestor)
16s and 18s have parts of the same nucleotide sequences – evolutionarily
important
Heirarchial Biological Classification (HBC): above class level is no longer valid
Scientific species name consists of:
1. The Genus name
2. The Species epithet (adjective modifying genus name)
3. The authorities of the name
Genus and species rank are the only names italicized
The Species Concept
The Morphological Species concept: looks different or is of a different kind defines a species
oThe traditional concept – developed as part of the pre-Darwinian “Natural” classification
The Mayr/Biological species concept: primarily applied to animals and stresses that species are
populations that reproduce naturally with their own kind (wolves and dog example)
oDeveloped by Ernst Mayr – an ornithologist
oThere are 3 main aspects to this concept:
1. Species are derived by shared derived traits rather than relative differences
2. Species consist of populations rather than unconnected individuals
3. Species are defined by their reproductive isolation producing viable offspring
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