Mechanisms: the processes of evolution

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Mechanisms the processes of evolution
Evolution is the process by which modern organis
ms have descended from ancient ancestors.
Evolution is responsible for both the remarkable
similarities we see across all life and the
amazing diversity of that life.
Fundamental to the process is genetic variation
upon which selective forces can act in order for
evolution to occur.
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Evolution only occurs when there is a change in
gene frequency within a population over time
Descent with modification. Compare these two
examples of change in beetle populations. Which
one is an example of evolution?
Low food supply
Color change
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Genotype versus Phenotype An organisms genotyp
e is the set of genes that it carries. An
organisms phenotype is all of its observable
characteristicswhich are influenced both by its
genotype and by the environment.
These two flamingos are genetically the same but
they are
different phenotypes. Why?
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Mutation, migration (gene flow), genetic drift,
and natural selection are the mechanisms of
evolutionary change.
A change in a DNA sequence, usually occurring
because of errors in replication or repair. What
is a ___________?
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However, natural selection and genetic drift
cannot operate unless there is genetic
variationthat is, unless some individuals are
genetically different from others. If all the
beetles are green, genetic drift and natural
selection cannot make brown ones.
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By studying the variety of happy-face spiders
that live on the different Hawaiian Islands,
researchers discovered intriguing patterns that
may help us to better understand how genetic
variation evolves.
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The happy-face spider is _____________ to these
four islands. It occurs nowhere else.
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Different forms ( ie___________ ) of the
happy-face spider. However, because all these
spiders freely mate, they are the same ________.
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The ratio of two yellow to one "other" occurs
generation after generation.
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Each island harbors the same sorts of morphs, and
the different morphs occur at the same frequency
(21) in each population.
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Why did each island have a 21 ratio of yellow to
other morphs? A first hypothesis involved
dispersal. Lets consider a number of theoretica
l models. Consider a bug population on two
islands...
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On this isolated island model, the population
starts with ___ blue and ___ yellow bugs. What
happens after twelve generations?
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On this isolated island model, the population
starts with ___ blue and ___ yellow bugs. What
happens after twelve generations?
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On this semi-isolated island model, the
population starts with ___ blue and ___ yellow
bugs, but ____ of the bugs are exchanged with
the other island. What happens after twelve
generations?
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On this semi-isolated island model, the
population starts with ___ blue and ___ yellow
bugs, but ____ of the bugs are exchanged with
the other island. What happens after twelve
generations?
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Continual exchange between islands maintains the
distribution.
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Therefore Dispersal HypothesisDispersal of
spiders between islands has caused a consistent
ratio of 2 yellow 1 "other" on all four
islands. This implies that these spiders have a
heritable trait that this 21 ratio is
maintained in the offspring. Molecular data we
re used to test this hypothesis.
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DNA RESULTS
The DNA results for the different islands are
depicted on this ______________. All of the
color morphs in one island population are more
closely related to each other than they are to
the color morphs from populations on other
islands.
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If dispersal between islands were common, we
would expect to find a close DNA relationship
between the spiders on the various islands.
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What does the DNA evidence say about the
Dispersal Hypothesis, that dispersal of spiders
between the Hawaiian islands has caused a
consistent ratio of 2 yellow1 other on all four
islands?
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According to the cladogram, the common ancester
of all happy-face spiders is most closely related
to the spiders on which island? ______________.
The Hawaii and Maui spiders have certain DNA
traits that are not shared by spiders on what
islands ? ________ and ________. The Molokai,
Maui and Hawaii spiders have DNA traits that are
not shared by spiders on _____________.
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Based on the cladogram, the common ancestor of
all the spiders evolved before the most recent
common ancestor of the spiders on Molokai, Maui
and Hawaii. Which island was the first to be
populated by the happy-face spider? _________.
Which island was second? __________ Can we tell
from the cladogram which was the third and fourth
to be populated ? ___.
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Which island is the youngest? Which is the
oldest? Which island has active volcanoes today?
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This linear formation is the result of the
movement of the Pacific tectonic plates over an
active hot spot in the earths mantle.
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As new islands formed, individuals from this
original population colonized subsequent islands
in a "hopscotch" manner. The youngest islands of
Maui and Hawaii were colonized last and harbor
the "youngest" populations of spiders.
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The spiders are so different genetically that
experiments show that even their selective
breeding characteristics differ from island to
island.
So the question still is why the 2 yellow to 1
other ratio on all the islands.
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The genetic mechanisms were different between the
spider populations on Maui and Hawaii.
The spider populations had evolved the same colo
r patterns and the same color pattern
frequencies, but they'd done it in totally
different ways! The question is why did all th
e islands independently evolve the same set of
color pattern traits.
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Could it be that the yellow morph has an
advantage in terms of camouflage and that natural
selection has made it more frequent than the
other morphs? Why not? If this were the case
, then the yellow morph would have greater
reproductive success and over time, would become
more and more frequent in the population. And
that's not what they observed. The populations
remained consistently at a 2 yellow1 other
ratio.
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Perhaps the more smiley spiders have a sexual
attraction advantage to balance against their
camouflage disadvantage..but these spiders are
color blind and they mate at night.
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Another idea is based on the observation that
animals often can find certain patterns/colors ea
sier than others. For example, which of the
following colors do most humans find most easily?
Why?
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Blue jays for example have trouble dividing their
attention among more than one task, such as
looking for more than one type of prey at the
same time.
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As the red prey become more successful, the jay
gradually changes to seek them out, allowing the
blue prey to recover.
Both red and blue prey are therefore maintained
in the population.
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The Hawaiian honey creeper preys on the
happy-faced spider. The current hypothesis is
that most of the time the creep is tuned to look
for the yellow spiders, but when their population
declines, the honey creeper reprograms to look
for the other types. In this way the 21 ratio is
maintained.
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Is the the 2-yellow to 1-other ratio in
happy-face spiders on all the Hawaiian islands a
homology or an analogy? What kind of genetic va
riation occurs in happy-face spiders?
What is a surprising observation about that vari
ation. Describe two early hypotheses that were p
roposed to explain the morph ratio in the
happy-face spider. Why did the dispersal hypot
hesis get rejected? Describe the current hypot
heses to explain her observations.
Why is genetic variation important to natural
selection?
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FINIS
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