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Allele to Trait Frequency

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    Okay. This problem can be a little tricky if you're
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    not used to figuring questions like this out, backwards. But
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    this is the best way to learn. Instead of giving
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    you all the numbers and have you plug them into equations,
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    it's better to have you work backwards like this. 'because
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    you really get to see the patterns that emerge. So
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    let's take the easy part first. We know that if
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    we have no lactase non-persistent, no lactose intolerant people, zero, 0%.
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    That represents our homozygous recessive condition. So
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    we gotta have zero in that group. There
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    are no people in our population that have that genotype. Okay, so now that means
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    we gotta split 1000 people between these
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    two genotypes, homozygous dominant and heterozygous. The only
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    scenario I can calculate that gives me this
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    particular allelic frequency is 500 in each group.
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    So remember both of these are lactase
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    persistent, so together that's everybody 100% are
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    lactase persistence. But we need a number
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    to get our allelic frequencies to 0.75 for
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    the dominant allele. And 0.25 for the recessive allele, so if we go to our
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    equation here and set it up toward backwards. 0.75 equals, we have the total
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    number of alleles, so how many total
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    dominant alleles are we dealing with here? This
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    would be X equals 1500. We've got to have 1500 dominant alleles in here. We do
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    the same thing with the recessive allele, we gotta have 500. Well, if we have to
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    have 500 recessive alleles. The only way I'm
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    going to get 500, is in this heterozygous condition.
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    'because I don't have any homozygous recessive. So
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    that means, to get 500 recessive alleles, I've gotta
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    have 500 heterozygous individuals so that I get
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    500 of these. 500 heterozygous individuals then makes up
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    500 of my dominants, as well. I need
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    1,500 total. So subtract 500 from 1,500. I need
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    1,000 more alleles. 500 in this box takes care
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    of 1,000, right? Because I get 500 of both.
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    500 of the first dominant and 500 of the second
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    dominant. Easy, huh? Or hard, depending on your perspective. I
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    really hope you understand this. If you don't, if you
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    have trouble, it's okay. There's not a lot of this course
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    that's going to deal with too much allelic frequencies. But I
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    do want to focus on it a bit more for the
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    rest of the lesson. If you can really get a
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    grasp of these allelic frequencies, you're going to have a whole new
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    appreciation for understanding gene flow, genetic
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    drift, and looking at huge populations of
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    individuals. And seeing how alleles travel
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    through. And can be shaped by evolution.
Title:
Allele to Trait Frequency
Video Language:
English
Team:
Udacity
Project:
BIO110 - Tales from the Genome
Duration:
02:48

English subtitles

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