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Announcements
Objectives
Web
Resources
Lecture
Activity
What is
Evolution?
Darwin's
Ideas
Natural
Selection
Examples
of
Microevolution
Types of
Natural Selection
Lecture
Syllabus
IB 100/101
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Announcements
Chapter 13, The Forces of Evolutionary Change:
Microevolution
Much of the material cited in this lecture outline came from
your
textbook. It is highly beneficial to read these chapters
carefully before your final exam.
You have open access (no log-in or password needed) to
instructional materials on the Text web site. Select "Resources" from the upper
left of the page and select the text chapter you want.
Moodle
You may also ask questions and see answers to your classmates'
questions in Moodle in the "Talk to Ed" forum.
Objectives:
The content of today's lecture will help you complete these
assignments:
After studying this material you should be able to:
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Describe biological evolution in terms of change in allele
frequency
in a population.
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Explain Darwin's main ideas concerning evolution by
natural
selection.
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Describe the evolutionary mechanism leading to the rise of
antibiotic resistant strains of bacteria, or the development of heavy
metal-tolerant invertebrates in Foundry Cove, NY, or industrial
melanism.
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Describe an example in which natural selection has
affected
the
virulence and/or spread of a human disease.
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Describe the results of directional, disruptive, and
stabilizing
selection.
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Explain the concept of balanced polymorphism and give an
example of
it.
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Understand the relationships among these terms:
| biological evolution |
natural selection |
microevolution |
| allele frequencies |
directional selection |
stabilizing selection |
| disruptive selection |
genetic variation |
balanced polymorphisms |
| mutation |
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Web Resources:
These links would provide good sources for Extra Credit Projects (due in Moodle 8:00 AM Thurs.
Apr. 30 )
or the Moodle Assignment #4 due at 8:00 AM Tuesday, May 5.
Lecture Activity
In our first lecture outline we considered qualities that
all living things share.
Work with one or two classmates to determine the
distinction
between these two qualities of living organisms.
Living things react to environmental change.
Living things adapt.
Write your distinction on a separate piece of paper.
Print AND sign your name.
Pass your paper to the aisle when requested.
What is Biological Evolution?
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The word, "Evolution", can be generally used to
describe any
sort of change.
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"Biological Evolution" is a term specifically
used
to
describe genetic change in a population over time, measured in
generations of the population.
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Hoefnagels, (Glossary - G8) defines "[Biological]
Evolution"
as, "Change in allele frequencies in a population over time."
An Example of Biological Evolution to Contemplate
Sex and the Single Guppy from PBS
Evolution
Series
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Click on "Simulation" in the lower right hand corner of
the
stream
illustration.
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Guppy Color Types -> Select "Even mix".
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Predator Species and Numbers -> Select "30 rivulus, 30
acara, 30
cichlid".
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Click "--> Run".
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Let the simulation run for several minutes - at least 10
generations
- and note the change in the proportions of the "Brightest", "Bright",
"Drab", and "Drabbest" male guppy color types.
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Individual male guppies may "REACT" to the predators by
attempting
to escape.
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The guppy population EVOLVES and ADAPTS to the presence of
high
predator populations over several generations.
Darwin's Main Ideas
Darwin's Observations of Nature
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Organisms are varied and some variations are inherited.
Within a species, no two individuals
(except identical
siblings) are exactly alike.
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More individuals are born than survive to reproduce.
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Individuals compete with one another for limited resources
that
enable them to survive.
Darwin's Inferences based on his Observations
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Within populations, the inherited traits of some
individuals make
them more able to survive and produce fertile offspring in the face of
certain environmental conditions.
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As a result of the environment's selection against
nonadaptive
traits, only individuals with adaptive traits live long enough to
transmit traits to the next generation. Over time, natural
selection can change the characteristics of populations, even
giving
rise to new species.
Natural Selection, Change in Allele Frequency, and
Microevolution
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Hoefnagels, (Glossary, pg G-14) defines natural
selection
as, "differential reproduction of organisms whose genetic
traits
better adapt them to a particular environment"
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More specifically, we mean a change in the number
(statistically
speaking, the "frequency") of individuals in a population that
carry one or two copies of a specific allele or variant of a specific
gene on their chromosomes.
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As we learned earlier in the course, an individual's
specific
versions of their traits are determined by the specific combination of
alleles they have for each gene locus. Those alleles came from
the individual's parents in the egg and sperm.
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Change in allele frequency in a popuation is called microevolution.
Microevolution can take place over a
relatively
short time periods (even one or only a few generations of a
population).
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Recall, a population is ".....a group of organisms
of one species
occupying a geographic location at the same time. The potential
for interbreeding defines the population's size". Hoefnagels, pg
788
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Hoefnagels glossary, pg. G-17 gives a slightly different
wording of the same concept, "members of the same species occupying a
region"
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Because an
individual cannot change his or her genes, we focus on populations as
the functional units of evolutionary change.
Some Examples of Natural Selection and Microevolutionary
Change
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Darwin's Finches (14 of them, each slightly
different, on islands that differ slightly in habitat).
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Industrial Melanism
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Evolution in Disease Organisms (Evolution occuring
right
now)
Infectious disease origin and transmission.
Emerging (new) and reemerging infectious diseases,
epidemics, and
antibiotic resistance all reflect selective pressures. Microorganisms
and viruses that cause infectious diseases are ever-evolving. Their
very
short generation times allow for more rapid mutation and genetic
recombination and the emergence of variants.
Earlier we talked about the mechanism of antibiotic
resistance in
bacteria. Remember the resistance genes on bacterial plasmids that
arise
by mutation and can be passed from bacterium to bacterium? Here we are
talking about how individual bacteria carrying these resistant genes
can
become more frequent in the population of bacteria, "swamping out" the
non-resistant bacteria.
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Evolution of Antibiotic Resistance, from PBS
Evolution
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What does this video have to do with evolution?
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Domesticating Diseases: Cholera and HIV, from PBS
Evolution.
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Evolution and bird flu, from the University of
California at Berkeley.
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Evolution and the way our bodies deal with disease,
a PDF file.
Types (Patterns) of Natural Selection:
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Directional Selection Hoefnagels figure
13.11A, pg 273.
Directional selection is selection against one extreme phenotype,
allowing another to gradually become more prevalent. An example of this
is industrial melanism, where some 100 species of insects have
undergone color changes enabling them to blend into polluted
backgrounds. Another example is the rise of antibiotic resistance.
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Disruptive Selection Hoefnagels figure
13.11B, pg 273.
Two extreme expressions of a trait each have a selective advantage, so
both persist. An example is white and tan snails living among white
barnacles on tan colored rocks; green colored snails are more often
seen
and eaten by predatory shorebirds.
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Stabilizing Selection Hoefnagels figure
13.11C, pg 273.
Stabilizing selection favors the survival and reproduction of
individuals with an intermediate form of a trait, because they have
greater survival and reproductive success. Extreme phenotypes are less
adaptive. An example would be selection for a median human birth
weight.
Babies that are too small have a lower chance of survival. Babies that
are too large at birth endanger the mother if C-section is not
available.
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Balanced Polymorphisms Is a form of stablizing
selection that maintains deleterious recessive alleles because
heterozygotes are protected against another medical condition.
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Maintains a potentially lethal genetic disease in a
population even
though the illness diminishes the fitness of affected individuals.
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The inherited disease persists because carriers
(heterozygotes) have
some health advantage over those who are homozygous dominant (and don't
have the disease).
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Malaria and Sickle Cell Disease (SCD). Also, see Hoefnagels figure 13.12 in your text. SCD
carriers, who do
not
have symptoms, are resistant to malaria. Bursting normal RBC's in those individuals who do
not have or carry SCD. The malaria parasite enters the cells,
reproduces, and eventually bursts the cells. In SCD carriers, about
half
the cells are sickled shaped. These cells are inhospitable to the
parasite. Over 35 generations, the frequency of the sickle cell allele
in East Africa rose from 0.1% to 45%.
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(Table 13.2, pg 274) Other Examples of Balanced
Polymorphisms
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Further explanation of balanced polymorphism, from
PBS Evolution and Ricki Lewis.
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