Today you will need
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Transcript of Today you will need
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Today you will need
•Something to write with.
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Evolution and Natural Selection
Continued
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The gradual change in a species over
time.
Evolution is…
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Things to keep in mind…
Populations, not individuals, evolve.
It’s all about the genes!
Occurs over a LONG period of time.
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Evidences of Evolution
Fossil Record
Biochemical - DNAComparative Anatomy
Biogeography
Observable Events
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How does evolution
occur?
Mechanisms of Evolution
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Bottleneck EffectAn event that kills off
a large number of members of a species randomly by chance therefore reducing
the genetic diversity.
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Bottleneck Effect
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Genetic DriftThe alteration of
allelic frequencies by chance events.
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Genetic Drift
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MutationsRandom genetic
changes that occur in a populations
DNA.
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Mutations Most mutations are bad
Some are advantageous
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Gene FlowThe transfer of alleles from one population
to another population through immigration
or emigration of individuals.
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Gene Flow
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A mechanism for change in a population.
Natural Selection is…
Survival of the FittestOrganisms with favorable
genetic variation survive to pass on their genes
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Types of Natural Selection
1.Stabilizing2.Directional3.Disruptive
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Stabilizing Selection:When the average is favored over
either of the extremes in a population.
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Stabilizing Selection:
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Directional Selection:This happens when one of the “extremes” is favored in an environment over the other extreme or the old average.
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Directional Selection:
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Disruptive Selection:This situation happens when
either extreme is favored over the average.
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Disruptive Selection:
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How are new species made?
Speciation: the evolution of a new species
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How are Species Made?Speciation is always caused by isolationTypes of isolation:
1. Geographic2. Reproductive
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Types of Isolation1. Geographic
IsolationA single species can become two different species because they are isolated by mountains, rivers, canyons, etc.
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Types of Isolation2. Reproductive Isolation
› Animals in different areas of the country may develop different actions and behaviors.
› These different behaviors can cause groups to separate from each other and become different species.
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Types of Isolation2. Reproductive
IsolationOrganisms may develop different mating seasons which do not correspond to one another
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Individuals die, species go extinct
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As the environment changes, organisms must have variations that allow them to survive (adapt) to those changes or dieIf an entire population of a species cannot adapt, that species becomes extinct.
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There have been at least 5 MASS extinctions during Earth’s history where a huge % of the living species were destroyed
At least one of these has been attributed to
meteor impact and its
consequences.
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