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← Allele to Trait Frequency

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Showing Revision 1 created 09/29/2013 by Cogi-Admin.

  1. Okay. This problem can be a little tricky if you're
  2. not used to figuring questions like this out, backwards. But
  3. this is the best way to learn. Instead of giving
  4. you all the numbers and have you plug them into equations,
  5. it's better to have you work backwards like this. 'because
  6. you really get to see the patterns that emerge. So
  7. let's take the easy part first. We know that if
  8. we have no lactase non-persistent, no lactose intolerant people, zero, 0%.
  9. That represents our homozygous recessive condition. So
  10. we gotta have zero in that group. There
  11. are no people in our population that have that genotype. Okay, so now that means
  12. we gotta split 1000 people between these
  13. two genotypes, homozygous dominant and heterozygous. The only
  14. scenario I can calculate that gives me this
  15. particular allelic frequency is 500 in each group.
  16. So remember both of these are lactase
  17. persistent, so together that's everybody 100% are
  18. lactase persistence. But we need a number
  19. to get our allelic frequencies to 0.75 for
  20. the dominant allele. And 0.25 for the recessive allele, so if we go to our
  21. equation here and set it up toward backwards. 0.75 equals, we have the total
  22. number of alleles, so how many total
  23. dominant alleles are we dealing with here? This
  24. would be X equals 1500. We've got to have 1500 dominant alleles in here. We do
  25. the same thing with the recessive allele, we gotta have 500. Well, if we have to
  26. have 500 recessive alleles. The only way I'm
  27. going to get 500, is in this heterozygous condition.
  28. 'because I don't have any homozygous recessive. So
  29. that means, to get 500 recessive alleles, I've gotta
  30. have 500 heterozygous individuals so that I get
  31. 500 of these. 500 heterozygous individuals then makes up
  32. 500 of my dominants, as well. I need
  33. 1,500 total. So subtract 500 from 1,500. I need
  34. 1,000 more alleles. 500 in this box takes care
  35. of 1,000, right? Because I get 500 of both.
  36. 500 of the first dominant and 500 of the second
  37. dominant. Easy, huh? Or hard, depending on your perspective. I
  38. really hope you understand this. If you don't, if you
  39. have trouble, it's okay. There's not a lot of this course
  40. that's going to deal with too much allelic frequencies. But I
  41. do want to focus on it a bit more for the
  42. rest of the lesson. If you can really get a
  43. grasp of these allelic frequencies, you're going to have a whole new
  44. appreciation for understanding gene flow, genetic
  45. drift, and looking at huge populations of
  46. individuals. And seeing how alleles travel
  47. through. And can be shaped by evolution.