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Genetic Variation & Natural Selection Within Populations 11.1 & 11.2
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Variation & Natural Selection What 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 1:30 1:00 :30 TIME!
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11.1 Genetic Variation Scenario: ◦ 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 Variation Genetic 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 Pool Defined: ◦ The combined alleles of all the individuals in a population. Why is it important: ◦ Where genetic variation is demonstrated Review: ◦ 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 Frequency A 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 Frequency How many blue eyed students? ◦ 8 students x 2 b alleles = 16 b alleles How 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 = 24 Total B alleles = 16 Total 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 Variation Mutation: ◦ 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 Version Parents 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 Traits Normal Distribution: ◦ Frequency is highest near the mean and decreases towards the extreme ends. Range of Variables FrequencyFrequency
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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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Microevolution Defined: ◦ The observable change in allele frequencies of a population over time. Natural Selections Role: ◦ Directional ◦ Stabilizing ◦ Disruptive Selection
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Directional Selection Defined: ◦ 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 Selection Defined: ◦ 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!!!
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