BIO122 Unit 2

What are the possible outcomes of hybridization?

• hybrid zones: selection may favor hybrids, or strengthen isolating mechanisms to reduce hybrids

• speciation: 3rd species

• Introgression: gene flow —> increase variation/adaptation, genetic swamping or fusion

• speciation via polyploidy

What is the species continuum?

a species is an interbreeding population of individuals with variation

What is allopatric speciation? What the two reasons as to why this occurs?

genetic divergence occurs due to geographic variation

1. gene pools of separated population divergence

• genetic drift (chance)

• different mutations arise

• lack of gene flow (migration)

• niches/selection pressures differ

1. reproductive isolation evolves as a by product of genetic divergence that results from selection or drift

What are examples of allopatric speciation?

• snapping shrimp: 15 pairs of sister species

• Harris’ antelope squirrel & white-tailed antelope squirrel

What is sympatric speciation?

genetic divergence occurs in the same area (no barriers)

What are examples of sympatric speciation?

• Galapagos finches

• Midas cichlid in Lake Apoyo, Nicaragua

  • one very deep lake with different niches

  • different diet, body morphology, & jaws

• Lake Victoria Africa: cichlid fish

  • clear water vs. murky water

  • predators, pollution (600 to 400 species)

• polyploidy

• allopolyploid

What is polyploidy?

• have more than two sets of complete chromosomes resulting from total gene duplication

  • ex: nondisjunction —> chromosomes fail to separate | MI = hp separate, MII = SCs separate

  • ex: aneuploidy —> abnormal number of chromosomes

What is allopolyploidy?

two species produce polyploid hybrid offspring

• ex: 30% of whiptail lizard species (52 species) are all female parthenogenic (reproduce without sperm)

• very little genetic diversity

• some are 2n, some are 3n

What is the punctuated equilibrium model? Who made this model?

An evolutionary theory proposing that species experience long periods of stability (stasis) with little change, "punctuated" by brief, rapid bursts of significant evolutionary change and speciation

Made by Eldridge & Gould

What are the two major mass extinctions?

• Permian extinction: ~250 mys 95% of all known species

• Cretaceous extinction: ~65 mya wiped out dinosaurs

What are causes of mass extinctions?

• climate change/glaciation, increased volcanic activity, asteroid impacts

What is ecological release?

a population boom with new species

What is the 6th mass extinction? Who coined the term?

Made by Nile Eldridge

• began 100,000 years ago when humans began dispersing

• got worse 10,000 years ago when humans began cultivating crops

• agriculture: most profound ecological change in the 3.5 mya of the history of life

• allowed humans to exceed carrying capacity of our ecosystem & overpopulate

What is the big band theory?

a phenomenon that provides evidence to suggest the universe started roughly 10-20 bya

What is the evidence for the big band theory?

1. expansion of the universe

2. abundances of He, D2O, Li (synthesized primarily in the first 3 min of the universe)

3. cosmic microwave background radiation: remnant heat from the Big Bang

When and where was the origin of the Earth?

approximately 4.6 bya condensed from matter/rocks

What is the early conditions for the origin of the Earth?

1. water vapor

2. H, N, NOx, CH4, NH3, H2S, CO2

3. no free O2

4. no life

5. colliding elements & molecules in water vapor

abiotic synthesis of organic compound & macromolecules

What did Miller & Urey do for their experiment in 1953?

• University of Chicago

• stimulated early conditions on Earth & supported the abiotic synthesis theory

• produced organic macromolecules (aa’s, sugars, lipids)

• worked under various conditions

  • spark of electricity

  • stimulated volcanic eruptions

  • hydrothermal & deep-sea vents

• extra terrestrial hypothesis:

  • Murcheson meteorite (4.5 bya) contains 86 aa’s including several L isomers on Earth

What are protobionts?

• membrane sac surrounding macromolecules (DNA/RNA) & metabolic agents

• possible characteristics of early living cells:

  • metabolism: anabolic & catabolic

  • plasma membrane: liposomes or vesicles from spontaneously from phospholipids in water

  • self-replicating

What are the properties of self-replicating molecules such as RNA?

• heat + coenzymes + phosphate chains = single strained enzymes

• ribozymes

• NS on ribozymes

  • copying introduces errors

  • more stable & faster copying variants would be more numerous

• RNA may have been a precursor to DNA, DNA is more stable

Describe the steps for the proliferation of life

• 3.8 bya: membrane-bound, self-replicating sacs of DNA & other macromolecules; lack of membrane-bound organelles

  • no O2: energy pathway = fermentation (only a few ATP)

• 3.5 bya: photosynthesis evolved in anaerobic prokaryotes

• 2.5 bya: O2 accumulated; cyanobacteria transformed the atmosphere (no chloroplasts)

What are the characteristics of an O2 rich atmosphere?

• aerobic respiration

• NO further chemical origin of living cells

• ozone layer (O2) —> protection of UV layer

Describe the evolution of eukaryotes?

• endosymbiosis: origin of mitochondria & chloroplast (possibly nucleus & cytoskeleton)

  • the host: an Asgard Archaean (Lokiarchaeota aka ‘Loki’)

  • the endosymbiont: an alphaproteobacterial

• serial endosymbiosis: origin of mitochondria (~1.2 bya) & chloroplast (~1 bya) —> cyanobacteria

What is the evidence for endosymbiosis?

mitochondria & chloroplasts vs. bacteria:

• very similar in size & structure

  • inner membrane of M & C are bacteria-like & have homologous enzymes & transport system

• have circular DNA that directs protein synthesis, is replicated independently of host cell DNA

• self-replicate by similar to cell division

  • M & C are not manufactured by a cell

M & C have their own ribosomes, which resemble those of bacteria more than eukaryotic ribosomes (in cytoplasm)

many antibiotics that kill or inhibit bacteria inhibit M & C protein synthesis (but not cytoplasmic protein synthesis in eukaryotes)

What is the evidence for DNA?

• Woese & Doolittle (1977) found:

  • mitochondrial DNA: Rickettsettia typhus bacteria DNA

  • cyanobacterial DNA: chloroplast DNA

• multiple molecular studies confirm genetic similarity

  • Rickettsiales bacterial DNA is a sister group to mitochondrial DNA

  • cyanobacteria DNA ancestral to chloroplast/plastid DNA

What are examples of contemporary endosymbiotic relationships?

• Paramecium bursaria: swallows photosynthetic green algae & stores them instead of digesting them

• hydra virdissima is green due to the symbiotic green algae Chlorella vulgaris which live within its body

• protozoans & termites

• giant amoeba Pelomyxa lacks mitochondria, have bacteria to make ATP

• corals, clams, & snails have algae endosymbionts

• human endosymbionts: e. coli, lactobacilli & other microbes in digestive tract

  • digestive plant material, protect natural flora in immune system

What is a chimera?

DNA of host cells + endosymbiotic organisms

**1st eukaryotic cells were genetic chimeras

What is the ‘Tree of Life’?

molecular evidence for repeated horizontal gene transfer

What are examples of fossils?

• insects in amber, frozen mammoths, & humans

• teeth, shell, & bones petrify or mineralize

• footprints, impressions, excrement (‘copralite’)

  • fossilized waste

What are the caveats to fossil formation?

• under heat & pressure, rock becomes metamorphic & fossils are destroyed

• soft-bodied animals & structures rarely leave fossils

  • EXCEPT FOR: Burgess Scale (invertebrate fossils)

What is a geologic time scale?

a transition period based on sequences of fossils in sedimentary rock

What are the four eras of the geologic time scale?

1. Cenozoic: 65 mya - present | age of mammals

2. Mesozoic: 240 - 65 mya | age of reptiles

3. Paleozoic: 570 - 240 mya | age of invertebrates, Cambrian explosion

4. Precambrian

What is a radioisotope?

a variant of an element with differing number of neutrons

What is a half-life?

“parent” decay into stable (“daughter") isotopes at constant, known rates

What is radioisotope dating?

comparing a ratio of radioisotope/stable isotope in a sample with that of a similar living organism

calculate time that radioisotope took to decay = approx. age of sample

to measure relative isotope abundance: isotope ratio mass spectrometry (IRMS)

Describe carbon dating

• C-14 common in atmosphere, plants, & organisms

• half-life of C-14 is ~5700 years (decays to N-14)

• date samples < 50000-60000 years old (= 8 half-lives)

Describe potassium-argon dating

• Potassium-40 (40K) decays to 40 Ar & 40 Ca

• half life of 40 K = 1.3 billion years

• measures from 4550 mya - 1000 years ago

How is uranium lead used for dating rocks & fossils?

• dates rocks from ~1 mya to over 4.5 bya

  • precision of 0.1-1%

• can date the age of Earth itself

How do the three domains correlate to the six kingdoms?

• Bacteria

  • Eubacteria (modern bacteria)

• Archaea

  • Archaebacteria (ancient bacteria)

• Eukarya

  • Protista (single-celled animals)

  • Fungi (mold & mushrooms)

  • Plantae (plants)

  • Animale (animals)

Trees (cladograms) are constructed based on…

shared homologous characteristics such as:

1. morphological sequences

2. DNA sequences

3. biochemistry (protein sequences)

What is the purpose of comparative DNA or biochemistry?

• to compare similarities that are the greatest among most closely related species

ex: cytochrome c —> the final electron acceptor in mitochondria

What is cladogenesis?

braching characteristic/pattern of diagram; continuing divergence

What is a clade?

• grouping of related organisms; ancestor & all of its descendants

What is a cladogram?

a diagram showing evolutionary relationships

What is a phylogenetic tree?

an evolutionary hypothesis/history being tested

What is the difference between simplesiomorphy & synapomorphy?

simplesiomorphy: shared ancestral/primative trait

synapomorphic: shared derived (modern) trait

• homologous traits

What are homoplasies?

shared characteristics that are analogous

i.e., evolved independently 2 or more times

What is a node in a phylogenetic tree?

a divergence point (speciation event)

monophyletic

clade groups with one common ancestor

paraphyletic

does not contain all descendants

polyphyletic

more than one ancestor

What is Occam’s razor?

• the most parsimonious tree is most likely (least # of assumptions)

• accounts for synapomorphies (genetic similarity) w/ fewest evolutionary events (fewest base changes)

What is a phylogram?

a geological time used to determine the relative distance of branches (time/molecular data)