## ← 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.