702 - Nat Selection
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| Artificial selection - | Breeding organisms with specific traits in order to produce offspring with identical traits
Example: dog breeds
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| Natural selection - | when individuals that have advantageous traits survive and reproduce at higher rates than individuals without those traits
this causes the species to evolve
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| Causes of natural selection - | overproduction, genetic variation, and competition
more offspring are produced than can survive; some have genetic traits that help them survive; these advantageous traits cause them to outcompete those without those traits
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| genetic variation - | genetic differences
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| Competition - | the struggle between organisms to survive in a habitat with limited resources
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| Adaptation - | A trait that helps an organism survive and reproduce
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| Galapagos finches - | Studied by Darwin
they live on different islands but they all evolved from the same ancestor
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| Allele frequencies - | how common an allele is in a population
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| Mutations - | a change in DNA
they happen randomly
Sometimes they cause a new, beneficial trait
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| Sexual reproduction - | when offspring are produced by two parents instead of one
This creates more genetic diversity within a species
This genetic diversity can help a species adapt to environmental changes
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| Speciation - | Formation of new species
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| species - | a group of organisms that can mate and produce viable, fertile offspring
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| viable - | can survive
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| fertile - | can have offspring
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| geographic isolation - | when populations of the same species are physically separated from each other
this prevents them from mating
as mutations build up in each population, they can become so different that they become different species
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| Adaptive radiation - | when populations of a single species spread out and become many different species
The Galapagos finches are an example
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| types of natural selection - | directional, stabilizing, disruptive
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| Directional selection - | occurs when natural selection favors an extreme version of a trait
example: favoring long tails over short tails
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| Stabilizing selection - | when both extreme versions of a trait are selected against
example: favoring medium-length tails over short or long tails
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| Disruptive selection - | when both extremes of a trait are selected for
example: favoring short and long tails but not medium tails
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