mechanisms of evolution. hardy-weinberg principle a. a population is in genetic equilibrium—all...
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Mechanisms of Evolution
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Hardy-Weinberg Principle
A. A population is in genetic equilibrium—all individuals are equally adapted to their environment & contribute equally to the next generation1. Five conditions for this to occur
a. No Genetic Driftb. No Gene Flowc. No Mutationsd. Mating must be randome. No Natural Selection
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Genetic Drift
B. Chance occurrences can cause an allele to become more or less common1. Founder Effect: result of migration (Darwin’s finches)
Ex. Amish and Mennonites: people rarely marry outside their own communities; Old Order Amish—high frequency of 6-finger dwarfism—can trace ancestry back to one of the founders of the order
2. Bottleneck: result of a dramatic reduction in population size and then rebounds; might be a possible factor in the potential extinction of a speciesEx. Cheetahs in Africa are so genetically similar they appear inbred; researchers think there was a bottleneck 10,000 yrs ago, and then again 100 yrs ago
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Gene Flow
C. Rate at which genes enter or leave the population—random migration naturally increases variation
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Nonrandom Mating
D. Organisms usually mate w/individuals in close proximity which promotes inbreeding
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Mutation
E. Some are harmful, some are advantageous
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Natural Selection
F. Acts to select those individuals that are best adapted for a particular environment
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Reproductive Isolation
G. Prevents gene flow among populationsEx. 2 species can mate to produce a hybrid
which is sterile (liger)**Other forms of isolation are more specific forms of this
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Speciation
H. Population diverges and new species is reproductively isolated
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Patterns of Evolution
A. Adaptive Radiation: many related species evolve from a single species (Darwin’s finches)—usually due to different environments Ex. guppies in a pool on the same river
B. Coevolution: 2 or more species change together
C. Convergent Evolution: 2 unrelated species have similar characteristics
D. Rate of Speciation: usually is gradual, but there have been periods of abrupt transitions
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Adaptive Radiation
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Coevolution
Acacia ants live in thorns of acacia tree. Plant make substance used by ants as food. Ants defend tree from herbivores by attacking/stinging any animal that brushes up against the tree
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Convergent Evolution
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Rate of Speciation