Lec22_Drift&Migration

Lec22_Drift&Migration - Flip the coin four times...

Info icon This preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Flip the coin four times. What is the probability of getting: 0 heads 0.0625 1 head 0.25 2 heads 0.375 3 heads 0.25 4 heads 0.0625 1 Flip the coin four times. Heads = A 1 allele. What is the probability of getting: 0 heads 0.0625 p = 0 1 head 0.25 p = 0.25 2 heads 0.375 p = 0.5 3 heads 0.25 p = 0.75 4 heads 0.0625 p = 1.0 1 highest probability outcome maintains p = 0.5 allele frequency, but certainly not guaranteed! = A1 p = f(A1) / 4 tosses !""#"$ &$$#'(&)*+ ,()- "&.+#/01 +"&,(.2 2&/*)*$ 3"#/ )-* 2*.* 4##0 2 N = 4 N = 2 ind. Most likely outcome, p = 0.5 5 5657 568 5687 569 5697 56: 56:7 56; 5 8 9 : ; p = 0 0.25 0.5 0.75 1.0 !""#"$ &$$#'(&)*+ ,()- "&.+#/01 +"&,(.2 2&/*)*$ 3"#/ )-* 2*.* 4##0 2 N = 10 N = 5 ind. 5 5657 568 5687 569 5697 56: 5 8 9 : ; 7 < = > ? 85 p = 0 0.2 0.4 0.6 0.8 1.0
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
!""#"$ &$$#'(&)*+ ,()- "&.+#/01 +"&,(.2 2&/*)*$ 3"#/ )-* 2*.* 4##0 2 N = 10 N = 5 ind. 5 5657 568 5687 569 5697 56: 5 8 9 : ; 7 < = > ? 85 p = 0 0.2 0.4 0.6 0.8 1.0 Probability of 10% reduction: f(A1) ! 0.4 = 0.38 !""#"$ &$$#'(&)*+ ,()- "&.+#/01 +"&,(.2 2&/*)*$ 3"#/ )-* 2*.* 4##0 2 N = 100 N = 50 ind. 5 5658 5659 565: 565; 5657 565< 565= 565> 565? 5 < 89 8> 9; :5 :< ;9 ;> 7; <5 << =9 => >; ?5 ?< p = 0 0.2 0.4 0.6 0.8 1.0 Probability of 10% reduction: f(A1) ! 0.4 = 0.028 Are coin tosses a good model for real populations combining gametes through mating? As strange as it may seem – YES! Random mating is equivalent to random pairing of gametes drawn from the gene pool It might seem like any success of A 1 getting into the next generation at the expense of A 2 would be, by definition, differential reproductive success indicating selection. @*.*A' B"(CD E*)F$ 2*) "*&0 A change due to selection would require that the A 1 allele contribute to phenotypic differences determining fitness advantages in A 1 A 1 or A 1 A 2 genotypes. If true, expect consistent change in f(A 1 ) rather than erratic chance effects. Expect deviation from genetic drift theory @*.*A' B"(CD E*)F$ 2*) "*&0
Image of page 2
time allele freq p 0 1 0.6 0.4 0.2 0.8 In any population with finite size (any real population), genetic drift will change the frequency of an allele randomly over time. time allele freq p 0 1 0.6 0.4 0.2 0.8 In any population with finite size (any real population), genetic drift will change the frequency of an allele randomly over time. time allele freq p 0 1 0.6 0.4 0.2 0.8 In any population with finite size (any real population), genetic drift will change the frequency of an allele randomly over time. With two alleles, the other allele is changing in step because p + q = 1.0 time allele freq p 0 1 0.6 0.4 0.2 0.8 In any population with finite size (any real population), genetic drift will change the frequency of an allele randomly over time. Which allele is more likely to become fixed?
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
time allele freq p 0 1 0.6 0.4 0.2 0.8 Clicker Question Which allele is more likely to become fixed? A.Dark green (currently at p = 0.7) B.Light green (currently at p = 0.3) C.Cannot determine under drift D.Both have equal probabilities time allele freq p 0 1 0.6 0.4 0.2 0.8 Clicker Question Which allele is more likely to become fixed? A.Dark green (currently at p = 0.7) B.Light green (currently at p = 0.3) C.Cannot determine under drift D.Both have equal probabilities A brand new mutation that arises in a population of N diploid individuals has an ultimate probability of fixation equal to 1/(2 N ) The probability that an allele will ultimately become fixed is equal to its current frequency in the population.
Image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern