Furry with a chance of evolution: Exploring genetic drift with tuco-tucos

1. Furry with a chance of evolution: Exploring genetic drift with tuco-tucos Jeremy Hsu, Mays Imad and Kerianne Wilson

2. Thought questions You track a population of tuco-tucos over time and notice that the trait (allele) frequency of a given gene changes over time, as shown above. • Do you think this population is evolving? • Do you think that this pattern can be due to 1) random processes, 2) nonrandom processes, or 3) both random and nonrandom processes?

3. Group Activity: Genetic Drift in Tuco-tucos • Work in groups of 2 or 3. • Each of your brown and white beans represents an individual tuco-tuco. The color represents the color of their pelage (i.e.: coat), a trait that does not affect their fitness and is not under natural selection.

4. Example of one generation Start with a population of 4 brown and 4 white beans.

5. Example of one generation For each generation, randomly select 4 individuals thatwill contribute their characteristics to the next generation.

6. Example of one generation For each generation, randomly select 4 individuals thatwill contribute their characteristics to the next generation.

7. Example of one generation Duplicate these 4 individuals to bring the population back to 8 tuco-tucos so population size remains constant.

8. Example of one generation Now record the total number of brown& white individuals in your table. Now repeat for five minutes!

9. Group Activity: Genetic Drift in Tuco-tucos • Start with 4 brown and 4 white beans. • For each generation, randomly select 4 individuals that will contribute their characteristics to the next generation. • Duplicate these 4 individuals to bring the population back to 8 tuco-tucosso population size remains constant. • Now record the total number of brown& white individuals in your table. • Repeat as many times as you canfor about 5 minutes.

10. Thought questions • How does the final ratio of bean colors in the population compare to what it was before you started? • If the ratio changed, was there a reason why it changed in the particular direction you observed, or do you think the change was random? Explain why.

11. Follow-up Group Activity: Genetic Drift in Tuco-tucos How might population size change the outcome?

12. Follow-up Group Activity: Genetic Drift in Tuco-tucos How might population size change the outcome? Predict how the color ratio would change across generations if the population had 100 individuals. Is fixation possible if a population had 1,000 individuals?

13. Ecological examples of the impact of genetic drift: Founder effect Huntington’s Disease Normal [Include photos of a normal brain and one from a person with Huntington disease] [Include map of South America depicting density of Huntington disease cases] Rare world-wide, but areas with high concentrations exist from founder effect http://web.stanford.edu/group/hopes/cgi-bin/hopes_test/population-genetics-and-hd/ For more information: http://web.stanford.edu/group/hopes/cgi-bin/hopes_test/the-basic-neurobiology-of-huntingtons-disease-text-and-audio/

14. Ecological examples of the impact of genetic drift: Founder effect Founding lizard limb length Lineage A Lineage B Lineage C Lineage D Lineage E Caribbean brown anole lizard experiment [Include a photo of a Brown Anolis lizard from the URL below of a layman press release of the study] https://www.sciencedaily.com/releases/2012/02/120202151127.htm Natural selection lead to the reduction in limb lengths for all lineages, but founder effect maintained the relative length of limbs among lineages Current lizard limb length Lineage A Lineage B Lineage C Lineage D Lineage E Original Science article: http://science.sciencemag.org/content/sci/335/6072/1086.full.pdf

15. Ecological examples of the impact of genetic drift: Bottleneck [Include map from Cheetah Conservation Fund] https://cheetah.org/about-the-cheetah/genetic-diversity/ • Results: • Poor sperm quality • Immune system homogeny • Kinked tails

16. Ecological examples of the impact of genetic drift: Bottleneck New Zealand Black Robin [Include conservation photos from URL below] [Include photo(s) of the black robin from the below URL] http://www.endangeredspecies.org.nz/store/doc/Black%20robin%20Endangered%20species%20factsheet.pdf https://toughlittlebirds.com/2013/03/29/the-incredible-story-of-the-black-robin/ Entire species descended from one male and one female. Results: No reported abnormalities yet

17. What we have learned... • Genetic drift causes evolutionary change and is a random process • Genetic drift acts more strongly on smaller populations • Genetic bottlenecks and founder effects are two real-life events that create smaller populations more susceptible to the effects of genetic drift.

18. Thought questions You track a population of tuco-tucos over time and notice that the trait (allele) frequency of a given gene changes over time, as shown above. • Do you think this population is evolving? • Do you think that this pattern can be due to 1) random processes, 2) nonrandom processes, or 3) both random and nonrandom processes? • How would your answer to questions 1 and 2 change if you knew the trait above was or was not being affected by natural selection?