Genetic Variation & Natural Selection Within Populations 11.1 & 11.2.
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Transcript of Genetic Variation & Natural Selection Within Populations 11.1 & 11.2.
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Genetic Variation & Natural Selection Within Populations11.1 & 11.2
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Variation & Natural SelectionWhat have we learned?At your table, take 2 minutes to
discuss what the take away message from our last chapter was. Determine your tables response & be prepared to share. 2:00
1:301:00
:30TIME!
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11.1 Genetic VariationScenario:
◦The zombie apocalypse has begun.◦The entire US is in horror and trying
to find ways to survive.◦What type of traits make you more
likely to be caught and changed into a zombie?
◦Does everyone you know have these traits?
◦What traits will make you less likely to be zombie food?
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Genetic VariationGenetic Variation
increases chance that some individuals will survive.◦Natural Selection acts on
phenotype in a population
◦Must have genetic variation to have different phenotypes
◦The greater the variation in phenotypes the greater the chance of survival.
Socially Awkward Penguin
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Gene PoolDefined:
◦The combined alleles of all the individuals in a population.
Why is it important:◦Where genetic variation is
demonstratedReview:
◦What is an allele?How do we determine the
frequency of an allele in a gene pool?
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WITH MATH!!!!
YAY!
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Allele FrequencyA class of 20 students all have either
brown (Bb or BB) or blue eyes (bb).◦8 students have blue eyes (bb = 8)◦8 students have a parent with blue eyes
(Bb = 8)◦4 students have no parent with blue eyes
(BB = 4) Assume these parents don’t carry recessive allele
◦What is the frequency of the blue eye allele in this class?
◦Hint: each individual allele counts as one in your total. (a blue eyed individual has 2 alleles for blue eyes)
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Allele FrequencyHow many blue eyed students?
◦8 students x 2 b alleles = 16 b allelesHow many brown eyed students with
recessive allele?◦8 students x 1 b allele = 8 b alleles◦8 students x 1 B allele = 8 B alleles
How many students (BB)◦4 students x 2 B alleles = 8
Total b alleles = 24Total B alleles = 16Total alleles in pop = 40
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Allele Frequency(B) allele freq is 16 / 40 = 40%(b) allele freq is 24 / 40 = 60%What would happen to the
frequency of B alleles if suddenly having blue eyes became an advantageous trait to humans?
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Sources of Genetic VariationMutation:
◦DNA change can lead to change in allele.
Recombination:◦Rearrangement of parent’s alleles
during gamete production
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Brain Break – The Music VersionParents hate your music….you hate
their music…why?As you age, your brain becomes
unable to handle as much dopamine.◦Dopamine: plays a major role in reward
driven learning. Gives you the “chills” when a new song you like comes on.
Because you fail to get that same sensation as you age, your music taste will become stagnate.
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11.2 Nat. Selection on Populations
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Distribution of TraitsNormal Distribution:
◦Frequency is highest near the mean and decreases towards the extreme ends.
Range of Variables
Frequency
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But Mr. Wilson, how does this Apply to Natural
Selection?Thanks for Asking!
Actually, for some traits, all phenotypes provide an equal chance of survival.
These phenotypes generally show a normal
distribution
Those that are the most common appear in the middle of the range.
Those that are less common are at the
extremes.
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But…If a trait in this distribution
becomes most favorable in nature…
The favorable phenotype will increase in frequency.◦This is natural selection
Can allele frequencies be observed over time? You betcha!
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MicroevolutionDefined:
◦The observable change in allele frequencies of a population over time.
Natural Selections Role:◦Directional◦Stabilizing◦Disruptive Selection
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Directional SelectionDefined:
◦Selection that favors one extreme of a trait’s range.
Example:◦Methicillin Resistant Staphylococcus
Aureus (MRSA)
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Lets Use Our Example
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Stabilizing SelectionDefined:
◦The intermediate phenotype is favored.
Example:◦Size of a newborn baby. ◦Too small = increased risks◦Too big = increased risks
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The Likely Trend
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Disruptive Selection Defined:
◦ When both extreme phenotypes are favored.◦ Intermediate phenotypes are selected against in
nature. Example:
◦ London’s Peppered Moth
Rural Industrial
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At this point:
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End of Notes!!!