Evolution

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Evolution

• All the changes that have transformed life from
  its earliest forms to what we see today.

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Evolution is the result of genetic changes that
occur in constantly changing environments.
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Natural Selection

• Populations change in response to their
  environment.
• Acts on phenotype of an organism.
• (Not genotype)

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Natural Selection

• Determines the differential survival of groups of
  organisms

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Phenotype

• Observable characteristics
• (green eyes, brown hair, purple flowers, etc.)

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Genotype

• Genetic makeup of an organism determined by a
  pair of alleles.

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Allele

• Alternative form of a gene for each variation of
  a trait.

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Gene

• Unit of hereditary information
• Located on a chromosome
• Contains DNA

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Gene Pool

• Total genes in a population at any one time

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Homozygous

• Having two identical alleles for a trait

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Heterozygous

• Having two different alleles for a trait

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Mutation

• Change in DNA of a gene or chromosome
• Mutations occur constantly in a gene pool

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Reproductive Isolation

• Prevention of mating between formerly
  interbreeding groups.
• or
• The inability of these groups to produce fertile
  offspring

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Geographic Isolation

• Physical barrier divides a population
• These two groups are not able to mate
• gt may lead to new species

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Speciation

• Formation of a new species

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Mass Extinction

• An episode in which many species suddenly become
  extinct

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Punctuated Equilibrium

• Evolutionary model
• Rapid changes to a species in a short time,
  followed by periods of little change.

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Gradualism

• Model of evolution involving slow, gradual
  changes to a species over time.

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Gradualism vs. Punctuated Equilibrium
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Bacteria

• First form of life on Earth
• Evolved 3.5 billion years ago (prokaryotes)
• Eukaryotes (complex) formed 1.5 billion yrs ago

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Multicellular life

• Evolved 570 Ma (Cambrian explosion of life!)
• Multicellular more than one cell
• Jellyfish-type creatures were first forms

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Vertebrates

• Have a backbone
• 1st were jawless fish
• Amphibians 1st on land
• Almost all land animals larger than a fist

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Arthropods

• Have an exoskeleton
• (Hard outer shell)
• First animals on land (scorpion)
• Crabs, lobsters, insects, spiders

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Reptiles

• Evolved from amphibians
• Diversified into many forms after the Permian
  mass extinction (250 Ma).

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Dinosaurs

• Evolved from reptiles and dominated the Mesozoic
  Era
• Were wiped out by a large body that impacted
  Earth 65 million yrs ago

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Mammals

• Were very small during the Mesozioc
• Became the dominant life form after the
  Cretaceous mass extinction (65 Ma)