Other Factors Can Affect Genetic Variation In A Population Natural Selection drives the evolution...
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![Page 1: Other Factors Can Affect Genetic Variation In A Population Natural Selection drives the evolution (change in genetic material) of a population Other factors.](https://reader035.fdocuments.us/reader035/viewer/2022062423/56649f1b5503460f94c30d9d/html5/thumbnails/1.jpg)
Other Factors Can Affect Genetic Variation In A Population
• Natural Selection drives the evolution (change in genetic material) of a population
• Other factors can cause changes in the genetic material (gene pool) of a population– Mutation– Migration– Assortative (nonrandom)
mating– Genetic Drift
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Genetic Drift
• Change In Allele Frequency Caused By Random Chance– Random chance =
natural disasters, disease, etc.
– Has a greater affect on small populations
– Often causes reduction in alleles present in the gene pool.
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The Bottleneck Affect
• A direct result of genetic drift– As a result of some
random event, several alleles are lost from a population.
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3 General Types of Natural Selection
1. Stabilizing Selection
2. Directional Selection
3. Disruptive Selection
1. Nature selects the average form of a trait (human baby size)
2. Nature selects one extreme form of a trait (e.g. only the very long tongue in anteaters, not the short tongue)
3. Nature selects both the extreme forms of a trait (e.g. very bright shell and very dull shell)
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The 3 Types of Natural Selection
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Sexual Selection: A Special Type of Directional Selection
• Individuals of one sex (usually males) of a species are more likely to get picked as partners by the other sex if their characteristics are bolder, brighter, louder or stronger than other members of the same sex.
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Of Course, Being More Noticeable Does Have Its Disadvantages . . .
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Before We Go On, An Important Question: What is a species?
• Members of a species are morphologically (physically) similar, and can successfully interbreed (produce fertile offspring).
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How Do New Species Form?
• Isolation• Isolating Mechanisms
– Prezygotic Isolation– Postzygotic Isolation
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Geographic Isolation
• Physical separation of members of a population (by formation of a canyon, mountain, river, etc.)– Leads to different
adaptations on each side of barrier, and eventually new species
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Geographic Isolation = New Species: An Example
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Reproductive Isolation• Species isolated
because they reproduce in different seasons or times of day
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Behavioral Isolation• Species Differ In
Their Mating Rituals (e.g. different bird songs, mating colors, dances, pheromones, etc.)
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Ecological Isolation• Ecological Isolation
– Species inhabit the same area, but different habitats, so they don’t encounter each other
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Mechanical
• Mechanical Isolation– Body structure
prevents mating – In layman’s terms - the
parts don’t fit– Famous quote in AP
Bio class at PHS• “You mean it’s like
trying to park a cadillac in an outhouse?”
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Reproductive Isolation
• Some barriers to successful breeding arise after fertilization and are called postzygotic isolating mechanisms– Sterile offspring (e.g.
Horse + Donkey = Mule)
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How quickly do new species form?
• 2 hypotheses– Gradualism
• Many transitional forms between common ancestor and modern organisms
– Punctuated Equilibrium• Sudden shifts in form from
an ancestor to newer organism, so not many transitional forms between common ancestor and modern organisms
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Patterns of Evolution
• Convergent Evolution
• Divergent Evolution– Adaptive Radiation– Artificial Selection
• Coevolution
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Convergent Evolution
• Organisms appear similar, but aren’t closely related
• Why?– Similar environment
selects for similar traits
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Divergent Evolution• Related populations
or species become less and less alike
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A Second Type Of Divergent Evolution
• Artificial Selection– Humans, rather than
nature, select traits
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Coevolution
• Two or more species in close association w/one another change together– Predator/Prey– Parasite/Host– Plant/Pollinator
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Finally – THE END!