Download Chapter 16 - Mrs. Pam Stewart

Bell Work
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Pick up plickers card
Pick up notes page for today (population
genetics)
Turn in Natural Selection worksheet #2 to
basket
Chapter 16
Population Genetics and Speciation
Mrs. Stewart
Advanced Honors / Honors Biology
Standard

CLE 3210.5.3 Explain how genetic
variation in a population and changing
environmental conditions are associated
with adaptation and the emergence of
new species.
Objective
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Define evolution in terms of alleles
Be able to calculate the allele frequency of a
population
Determine how the 5 Hardy Weinberg factors
affect allele frequencies
Goldfish Lab
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Each group should obtain the following items:
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1 Paper towel (this will be your “pond”)
10 pretzel goldfish
10 regular goldfish
10 parmesan goldfish
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Keep goldfish on paper towel
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Population Genetics
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The study of evolution from a genetic point of
view
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Microevolution: change in the allele
frequencies of a population
Variation Within a Population
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All populations
show variations in
their traits
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Different shaped
beaks
Different colors
Different athletic
abilities
Different immune
system responses
Sources of Variation
Within a Population
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Variations in the genotypes of a population arise
by:
 mutation – changes in genes that occur either
naturally or influenced by environment
 Passed to offspring if occurs in gametes
 Recombination – the law of independent
assortment (chromosomes) and crossing over
during meiosis
 random pairing of gametes (sexual
reproduction) – organisms produce large
numbers of gametes, so the union of a particular
pair is strictly by chance.
The Gene Pool
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The total genetic information available in a
population is called the gene pool.
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In other words: All of the possible alleles
(variations) that are present, for each gene,
within a population
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Frogs in a pond
Trees in the forest
People in a town
**This is not a real place – it’s an abstract
idea – an imaginary collection
Allele Frequency
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Allele frequency is
the number of times
an allele occurs in
the gene pool
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This is in
comparison to how
often the other
alleles occur too
Relative Allele Frequencies
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determined by dividing the total number of a
certain allele by the total number of alleles of
all types in the population
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Total number of a certain allele___
total number of all alleles in a population
Expressed as a percentage or a decimal.
Activity
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Discover the allele frequency for brown
(pretzel) fish.
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Add up the total number of all alleles in your
population of fish
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Brown fish (pretzel) = BB
Orange fish (regular) = Bb
Yellow fish (parmesan) = bb
Divide the number of “brown” alleles by the total
number of alleles.
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Evolution is any change in the
relative frequency of alleles in a
population.
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Remember: Populations, not
individual organisms, evolve over
time.
Allele frequencies in the gene pool
do not change unless acted upon by
certain forces.
Five conditions that affect the
relative frequency of alleles
1.
2.
3.
4.
5.
Genetic mutations
Gene flow
Genetic drift
Nonrandom mating
Natural selection
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This is known as the
Hardy Weinberg
Genetic Equilibrium
model
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used to determine and
understand the forces
that act upon genetic
equilibrium
1. Mutations
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Mutations are changes in the DNA.
2. Gene Flow
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The flow of genes between
populations
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Emigration and immigration cause
gene flow between populations and
can thus affect gene frequencies.
Immigration vs. Emigration
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Immigration: Gene flow INTO a population
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Emigration: Gene flow OUT of a population
Activity
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Immigrate: 10 yellow fish move in from a
neighboring pond
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Emigrate: 5 brown fish move out to another pond
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Recalculate the brown allele frequency
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Question: How does immigration or emigration
affect allele frequencies in a gene pool?
Human
Evolution
from Gene
Flow
3. Genetic Drift
Genetic drift is a change in allele
frequencies due to random events.
 Genetic drift operates most strongly
in small populations.
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Think – pair - share
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What are some other random events that could
affect allele frequencies in a population?
Activity
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Genetic Drift: Perform a random act to your
population
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Recalculate the brown allele frequency
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Question: How does genetic drift affect allele
frequencies in a gene pool?
Random Mating
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Do humans randomly
mate?
 No.
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Random mating:
happens more by
chance and not by
choice (has less effect
on allele frequencies)
4. Nonrandom Mating:
Sexual Selection
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Mating is nonrandom whenever
individuals may choose partners.
Sexual selection occurs when certain
traits increase an individual’s success at
mating.
Sexual selection affects the allele frequencies
of a population.
Courtship ritual
Activity
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What if every fish in your “pond” only wants
to mate with an brown fish?
What would that do to your allele frequencies?
5. Natural Selection
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The ongoing process in nature where the
presence or absence of certain factors in the
environment “select” which traits/variations
within a population are most successful
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Most traits are polygenic = many variations
Without
Natural
Selection,
polygenic
traits
maintain a
bell curve
With Natural Selection…
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Three general patterns
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Stabilizing Selection
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Disruptive Selection
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favors the formation of average traits.
favors extreme traits rather than average traits.
Directional Selection
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favors the formation of one of the extreme traits.
Exit Ticket
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How does evolution by natural selection
depend on variation within a population?
Complete Types of Natural
Selection practice sheet
JELLY BELLICUS LAB
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COMPLETE JELLY BELLICUS ACTIVITY
AND CREATE GRAPHS
Exit Ticket: (for jellybellicus lab)
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I gave you 3 examples of natural selection
patterns in this lab. The environmental factors
in nature determine “fitness” in natural
selection.
Come up with an example using the jelly
bellicus species and the crew members to show
artificial selection occurring.
Bellwork – which natural
selection pattern is represented?
The Concept of Species
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Biological species concept
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a species is a population of organisms
that can successfully interbreed but
cannot breed with other groups
Isolation and Speciation
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Geographic Isolation
 Results from the separation of population subgroups
by geographic barriers.
 Allopatric Speciation
 Speciation due to separation of subgroups of a
population – geographic isolation
Reproductive Isolation
 Results from the separation of population subgroups
by barriers to successful breeding.
 Sympatric Speciation
 Reproductive isolation within the same geographic
area
Allopatry vs Sympatry
http://deltabiology.com/wp-content/uploads/2012/02/Sympatry.jpg
http://scienceblogs.com/evolvingthoughts/allopatry.jpg
Reproductive isolation:
Monkeyflower
http://faculty.washington.edu/toby/images/mim29%20Nature.jpg
Reproductive isolation sympatric
http://evolution.berkeley.edu/evolibrary/images/evo/drosophila_scene7.
gif
Rates of Speciation
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Gradualism
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species undergo small changes at a constant rate.
Punctuated equilibrium
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new species arise abruptly, differ greatly from their
ancestors, and then change little over long periods.