Biology - Evolution

Term 4, Introductory genetics (2011)

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  • Created by: Alysia
  • Created on: 26-11-11 06:10

What are the basic ingredients for life?

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A source of energy, carbon and liquid water.

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How will sampling the chemical makeup of a comet assist us in understanding life's origins?

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May provide an understanding of how the first organic molecules formed and whether comets could have carried them to Earth.

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What are the three most accepted scientific views for the origin of life?

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Ocean surface, Panspermia and Undersea thermal vents

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Summarise the Ocean surface theory:

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- Life started in a tidepool, pond or on moist clay
- UV/lightning would have energised volcanic gases to form prebiotic molecules in the froth

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Summarise the Panspermia theory:

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- Living organisms were seeded on Earth from comets and meteors

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Summarise the Undersea thermal vents theory:

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- Life arose at thermal vents
- Volcanoes provided the anoxic (without oxygen) environment and necessary gasses, energy and catalysts for the formation of prebiotic compounds.

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How did the discovery of ribozymes assist in creating a plausible model for the prebiotic origin of life?

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Ribozymes can act as both genes and enzymes, therefore a plausible model could be created as RNA can perform the catalytic activity needed to assemble themselves. They could them synthesize proteins. Without a molecule with this dual ability genes could not be formed without enzymes, and enzymes (proteins) could not form without genes.

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How old are the oldest known fossils of microscopic life?

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3.5 billion years old (cyanobacteria).

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What were the organic molecules produced in the Miller-Urey experiment?

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Amino acids.

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How old is the first firm evidence of eukaryotic cells?

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540-600 million years old.

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What is the endosymbiosis theory?

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Eukaryotic cells evolved from large prokaryotic cells that ingested other free-floating prokaryotes. These formed a symbiotic relationship.

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What are the two most important organelles that were developed as a result of this?

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Mitochondria (for aerobic respiration) and Chloroplasts (for photosynthesis in aerobic conditions

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What evidence of this theory is there?

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Both the mitochondria and chloroplasts retain their own self-replicating circular chromosome

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Eons and eras:

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Precambrian (Archaean, Proterozoic) 4600 – 570 mya
Origin of Earth, photosynthetic bacteria, protists, fungi, algae and animals

Paleozoic (Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian)550 – 240 mya
Early – Origins of animals with hard parts, simple marine communities
Late – Adaptive radiations of marine invertebrates and fish, origin of reptiles, insects and spore bearing plants, mass extinction

Mesozoic (Triassic, Jurassic, Cretaceous) 240 – 65 mya
Adaptive radiation of marine invertebrates, dinosaurs and fishes, origin of mammals, mass extinction

Cenozoic (Tertiary, Quaternary) 65 mya – now
Major climate shifts, adaptive radiations of angiosperms (flowering plants), insects, birds and mammals.

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What is adaptive radiation?

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A surge of evolution from an original ancestral form as new forms ‘fan out’, adapting over time to new niches. The classic example must be the fourteen Galapagos finches examined by Darwin, all presumably descended from a common ancestral species, but each of which had a different mode of life.

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What are and what is the importance of transitional fossils?

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Transitional fossils are those possessing a mixture of the characteristics of two different, but related, taxonomic groups. They are important because they indicate that one group may have given rise to the other via evolutionary processes

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What is the importance of fossils as a record of evolutionary change over time?

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Fossils can be compared to living species today therefore giving an insight into their evolution.

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3 major mass extinctions:

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The Permian (225 mya) extinction of nearly all life on Earth

Cretaceous (65 mya) more than 50% of marine species and many families of terrestrial plants and animals including most dinosaurs

Megafaunal/pleistocene (10000 yrs ago) extinction of giant mammals

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What is natural selection?

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A process in nature in which organisms possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency, and therefore, are able to transmit and perpetuate their essential genotypic qualities to succeeding generations. Originally proposed by Charles Darwin, natural selection is the process that results in the evolution of organism.

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What is needed of natural selection to occur?

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Overproduction and variation

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What are the three types of Natural selection?

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Stabilizing selection acts against phenotypes at both extremes of the distribution, favouring the multiplication of intermediate phenotypes. 

Directional selection acts against only one extreme of phenotypes, causing a shift in distribution toward the other extreme.

Diversifying selection acts against intermediate phenotypes, creating a split in distribution toward each extreme.

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Which leads to evolution?

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Directional, as it changes the gene pool over a period of time.

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Prezygotic isolating mechanisms

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Spatial (geographical), temporal (including seasonal), Ecological (habitat), Gamete mortality, Behavioural (ethological), Structural (morphological)

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Postzygotic isolating mechanisms

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Hybrid serility, Hybrid inviability, Hybrid breakdown

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What use do reproductive isolating mechanisms have?

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It protects the gene pool from the diluting and potentially adverse effect of genes being introduced from outside the species (species are often finely tuned to their niche; altering their phenotype by introducing foreign genes will usually reduce survival and fitness

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Allopatric speciation:

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one species divides into two because the original homogenous population has become separated and both groups diverge from each other. 

In their separate niches, the two groups go their own evolutionary ways, accumulating different gene mutations, being subjected to different selective pressures, experiencing different historical events, finally becoming incapable of interbreeding should they ever come together again.

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Sympatric speciation:

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Sympatric speciation refers to the formation of two or more descendant species from a single ancestral species all occupying the same geographic location. In sympatric speciation, species diverge while inhabiting the same place.

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