how evolution occurs genetically. evolution occurs in _populations_ not _individuals. why? within...
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THEORY OF EVOLUTION II
How Evolution Occurs Genetically
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HOW EVOLUTION WORKS Evolution occurs in _populations_ not
_individuals. Why? Within the _lifespan_ of one
individual, new features cannot evolve in
response to _natural_ selection. Only as
traits are inherited, can the _environment select for them
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GENETIC EQUILIBRIUM _gene_ _pool_ is the entire collection of
genes in a population.
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GENETIC EQUILIBRIUM If you know the genotypes of a population,
you can calculate the _allelic _frequencies, or the percentage of an
allele in a population. When the frequency of alleles is not
changing from generation to generation the
population is in _genetic_ _equilibrium.
When allelic frequencies are changing, the population is evolving.
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WHAT CAUSES GENETIC CHANGE Hardy-Weinberg postulated that
populations WILL NOT change allelic frequenices if these five conditions are met:
A. No Mutation B. Large population C. No migration D. Random mating E. No natural selection
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WHAT CAUSES GENETIC CHANGE _Mutation___ is any change in DNA. While
most
often _harmful in some cases it can be _beneficial_.
Causes: a. _chemicals____ b. _radiation___ c. _DNA replication errors__
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WHAT CAUSES GENETIC CHANGE 2._genetic _drift is random change of allelic frequencies due to _chance. More important in
_small_ _populations_ than large ones. For example, there is village in Spain that is
polydactyl, that recessive gene shows up in a much larger percentage_ than normal due to chance.
Continued inbreeding in the same population _concentrates_ the trait.
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GENETIC DRIFT
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WHAT CAUSES GENETIC CHANGE 3. _Migration___ Individuals _enter_ or _leave_ a
population
either adding or subtracting alleles from a population.
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WHAT CAUSES GENETIC CHANGE 4. Sexual selection is non-randoming
mating, which can result in dramatic evolution of certain traits.
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WHAT CAUSES GENETIC CHANGE 5. Natural selection will always cause
allelic change due to survival differences.
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HOW NATURAL SELECTION ACTS ON POPULATIONS Variations tend to go over a _range. Ex – Height of people. Selection occurs when _one area__ of
traits are favored
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NATURAL SELECTION 1. Stabilizing __selection__ is when
average individuals in a population are favored. This reduces __variation_ in a population
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NATURAL SELECTION 2. directional _selection is when one extreme form of the trait is favored.
This can lead to rapid _evolution in a population.
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NATURAL SELECTION 3. disruptive _selection_ is when
selection favors both the extreme forms of a variation. May lead to new _species_.
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EVOLUTION OF SPECIES A _species are organisms that basically
look
similar and can have fertile offspring. _speciation_ is the evolution of a new
species.
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EVOLUTION OF SPECIES 1. geographic isolation is when a
physical
Barrier separates two groups leading to _unique gene pools. _Australia__
is considered a good example of this
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EVOLUTION OF SPECIES 2. _reproductive_ isolation is when
Formerly interbreeding organisms no longer produce viable offspring. Happens in two ways:
_reproductive, genetic differences lead to
death of embryo. seasonal, animals start breeding at
different times of the year based on their environment.
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EVOLUTION OF SPECIES 3. polyploidy is when, during meiosis,
extra
chromosomes are added to the genome. This is seen in plants. Perhaps _half_ of
all flowers_ and _crops_ are polyploid.
It
leads to new species instantly.
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GRADUALISM V. PUNCTUATED EQUILIBRIUM 1. ._gradualism is the idea that species
develop through the slow buildup of
adaptations. This was _Darwin’s_ view.
However, many species have been amazingly stable over time.
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GRADUALISM V. PUNCTUATED EQUILIBRIUM punctuated equilibrium says that
living
Things have long periods of stability with speciation that occurs in rapid bursts. This is
caused by changes in the environment
or introduction of new alleles.
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CONVERGENT V. DIVERGENT EVOLUTION . convergent evolution is when two
species
evolve similar adaptations in different locations. This happens with geographic isolation
Ex. Rabbits and patagonian hares_
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CONVERGENT V. DIVERGENT EVOLUTION 4. divergent evolution is when two
species grow less alike over time due to reproductive isolation.
Ex. African and Asian elephant