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Genetic Drift and the  Founder Effect  A Collaborative Online Activity for Students of Evolution <ul><li>Dr Janet Haresnap...
 
Diverse population: ten different genes represented by 10 different coloured beads
Small number of insects lands on an island – bringing pink, blue, white purple, red and black genes only
<ul><li>Small founder population 21 </li></ul><ul><li>Andrew (AA) </li></ul>Parent population and six small founder popula...
Founder population, initially (above).  After time (right), most genes have multiplied but black has been lost
                    7 7 6 6   Allelic Diversity (Number of different alleles)                     12 12 14 15 Total       ...
<ul><li>How do populations on each island differ? </li></ul><ul><li>NC: the populations on each island are likely to diffe...
2. How does genetic diversity of  founder populations differ from the parent population? MS: Genetic diversity is much red...
Evolution as a result of genetic drift
Large founder population Here the number of individuals reaching the island is larger Contains all ten different genes fro...
10 10 10   10 10 10   Allelic Diversity 127 126 121   111 148 131 Total  17 15 8   8 18 10 dark blue 19 14 19   15 11 17 y...
3. Likelihood of allele being represented in the founder population  - does this depent on the size of that founder popula...
4. Implications for the genetic diversity ? DD: There will be less genetic diversity of the population which has originate...
Estimates of Genetic Differentiation 0.103 0.101 0.101 0.102 F ST Parent v Large founder population 0.115 0.112 0.116 0.12...
Estimates of Genetic Differentiation                     0.101 correct 0.101 c orrect 0.103 correct 0.101 correct 0.101 co...
Look at the values of F ST  of the large and small founder populations    1 . Effect of size of the founder population on ...
S366 Students trialled the activity in a tutorial
Founder Effect activity – summary <ul><li>First trialled as a tutorial activity in 2008 </li></ul><ul><li>Piloted as an on...
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A Collaborative Online Activity For Students Of Evolution

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A presentation about an activity on genetic drift and the founder effect, designed for students of evolution. It is a collaborative online activity in which participating students add their observatiosn to a wiki.

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A Collaborative Online Activity For Students Of Evolution

  1. 1. Genetic Drift and the Founder Effect A Collaborative Online Activity for Students of Evolution <ul><li>Dr Janet Haresnape </li></ul><ul><li>Department of Life Sciences </li></ul><ul><li>Open University </li></ul>
  2. 3. Diverse population: ten different genes represented by 10 different coloured beads
  3. 4. Small number of insects lands on an island – bringing pink, blue, white purple, red and black genes only
  4. 5. <ul><li>Small founder population 21 </li></ul><ul><li>Andrew (AA) </li></ul>Parent population and six small founder populations - Each student claims one island
  5. 6. Founder population, initially (above). After time (right), most genes have multiplied but black has been lost
  6. 7.                     7 7 6 6   Allelic Diversity (Number of different alleles)                     12 12 14 15 Total                     1 1 0 2 dark blue                     1 1 0 0 yellow                     0 3 2 0 green                     1 0 3 2 purple                     4 4 2 0 orange                     2 0 1 5 white                     0 1 4 4 pale pink                     1 0 0 0 bright pink                     2 1 2 1 black                     0 1 0 1   red                     JCi RB AA TAG Your intiials   Founder Populations record number of each allele     Allele colour
  7. 8. <ul><li>How do populations on each island differ? </li></ul><ul><li>NC: the populations on each island are likely to differ slightly in size and gene composition ( Spot on!) </li></ul><ul><li>AD: E ach island will have a different population due to chance   (Yes) </li></ul><ul><li>MS: Over time more numerous alleles in the founder populations will tend to become fixed at the expense of less numerous initial alleles, so that island populations will tend to differ more from each other. (This may well happen - perhaps someone might like to comment on the relationship between the rate of change due to genetic drift and the size of the founder population?) </li></ul><ul><li>TAG: Evolution by genetic drift will be faster for smaller population sizes. (Yes) </li></ul><ul><li>EA: The occurrence of alleles on each island is the result of a random process and hence there will be no particular pattern to the allele distribution. (Absolutely correct) </li></ul>
  8. 9. 2. How does genetic diversity of founder populations differ from the parent population? MS: Genetic diversity is much reduced in founder populations and will tend to become further reduced with possible extinctions (Yes - you might mention that this would be a predicted outcome of a lot of genetic drift) .   BR: They'll be severely reduced, one founder population has only 50% of the original number of alleles available (Well spotted - this population has an allelic diversity of only 5 and this means as you say that 50% of the alleles present in the parent population have been lost in the founder population) EA: Because only a sample of the alleles from the parent population have moved to the island the founder populations will be much less genetically diverse thanthe parent population.
  9. 10. Evolution as a result of genetic drift
  10. 11. Large founder population Here the number of individuals reaching the island is larger Contains all ten different genes from parent population: Allelic diversity is 10
  11. 12. 10 10 10   10 10 10   Allelic Diversity 127 126 121   111 148 131 Total 17 15 8   8 18 10 dark blue 19 14 19   15 11 17 yellow 9 18 11   11 18 15 green 15 9 13   10 13 14 purple 16 11 17   15 14 11 orange 10 12 6   9 8 10 white 12 16 11   8 17 14 pale pink 11 9 9   11 17 17 bright pink 6 14 17   16 13 17 black 12 8 10   8 19 6   red MT NC CB   TAG JO JH Your intials   Founder Populations record number of each allele     Allele colour
  12. 13. 3. Likelihood of allele being represented in the founder population - does this depent on the size of that founder population? DD: yes the greater the size of the founder popultation, the greater the likelihood of an allele being represented in that founder population. (Yes - so what does this tell us about genetic drift?) MT: Yes. I now have all 10 diff. alleles present, while in the small one I had only 7 diff. ones   (Brilliant - you have quoted the difference in allelic diversity from 7 in the small founder population to 10 in the large founder population) EA: Yes - the increase in population size increases the chances that a particular allele will occur in the founder population.
  13. 14. 4. Implications for the genetic diversity ? DD: There will be less genetic diversity of the population which has originated from a very small number of founder individuals Correct!) , NC: In small populations the alleles will become either fixed or lost by random genetic drift much quicker than a larger population (brilliant - genetic drift is more likely to be significant in a smaller population as you say) BR: the lower the genetic diversity the greater the chance that low frequency alleles may be lost - reduced options = reduced opportunity for rapid adaptation in changing environments which may increase the risk of extinction.   (as above, this is brilliant - a perceptive comment)
  14. 15. Estimates of Genetic Differentiation 0.103 0.101 0.101 0.102 F ST Parent v Large founder population 0.115 0.112 0.116 0.128 F ST Parent v Small founder population DW TG NC JH Initials
  15. 16. Estimates of Genetic Differentiation                     0.101 correct 0.101 c orrect 0.103 correct 0.101 correct 0.101 correct 0.102 F ST         0.893 0.895 0.893 0.896 0.894 0.893 H e for large founder pop Parent v Large founder population         0.135 correct 0.109 correct 0.115 correct 0.112 correct 0.116 correct 0.128 F ST                     0.773 0.867 0.848 0.853 0.847 0.800 H e for small founder pop Parent v Small founder population       TAG  JO DW TG NC JH Initials
  16. 17. Look at the values of F ST of the large and small founder populations   1 . Effect of size of the founder population on genetic differentiation between parent and founder populations? NC: The smaller the founder population, the larger the value of F ST . This means the smaller founder population shows a greater degree of genetic differentiation from the parent population than the larger founder population does . (Spot on!) DW: Seems to be a greater genetic differentiation in small population as F ST is greater value. (Yes this is the genetic differentiation between the small founder population and the parent population) (What about the value of looking at several small and several large founder populations in this activity? )
  17. 18. S366 Students trialled the activity in a tutorial
  18. 19. Founder Effect activity – summary <ul><li>First trialled as a tutorial activity in 2008 </li></ul><ul><li>Piloted as an online activity with small group of students in 2009 </li></ul><ul><li>Made available mid-May 2010 to all students on S366 (Evolution) as a voluntary exercise </li></ul><ul><li>Twenty-two students participated in the activity online in the first 2 weeks (by 1 st June) </li></ul><ul><li>More are adding to the wiki each week </li></ul><ul><li>Will be available until course ends in October 2010 </li></ul>

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