Genetic Drift Lab: Founder Effect vs. Bottleneck Effect using Skittles

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1 Name: Date: Genetic Drift Lab: Founder Effect vs. Bottleneck Effect using Skittles Background: Genetic Drift is defined as the random change in allele frequencies that occurs in small populations. It is not due to natural selection. Genetic drift is strongly tied to population size and becomes important in situations where a small segment of an original population splits off or becomes isolated from the parent population. A change in allele frequencies as a result of this migration of a small subgroup of a population is known as the founder effect. Other times this process occurs when the original population undergoes a devastating population reduction (i.e. by natural disaster) and the allele frequencies are changed as a result. This is referred to as the bottleneck effect. Evolution at the population level is defined as a change in allele frequency over time. This lab will demonstrate how genetic drift can be a strong evolutionary force in certain situations. We will see that a smaller population size can show a much more dramatic shift in allele frequencies over time due to these two events. Initial Population: 1. Pick a cup of 24 skittles and a paper towel; this represents the original population of a group of organisms known as Candus spectacularus. Each colored skittle represents one allele found in the population. Note that there are 5 possible alleles represented in this population (multiple alleles). 2. Count the alleles in your initial population and fill-in the data in Table #1. 3. Use the following formula to calculate Allele Frequency: Allele Frequency (%) = total # of each allele x100 total # of all alleles Founder Effect: 4. WITHOUT LOOKING remove 6 Skittles from the cup and place them on the paper towel; this represents the founding group. The founding group has left the original population to start a new population. How did this emigration by the founding group affect the allele frequencies seen in this new population? (Discuss) Record all the data in Table #2. 5. Now, put the 6 Skittles back into the cup. We will now study the bottleneck effect on this original population. Bottleneck Effect: 6. Without looking, remove 18 Skittles. This removal represents a natural disaster that has hit the Candus spectacularus population. A hurricane has wiped out most of the members in this population. Only 3 individuals remain, each having 2 alleles (6 alleles total). What do the allele frequencies look like after this disaster? (Discuss) Record all the data for Table #3.

2 Discussion Questions (answer on a separate piece of paper): 1. How is an allele frequency different than a genotype? 2. Define genetic drift. 3. Define founder effect. 4. Compare Table #1 to Table #2. Compare allele frequencies for each allele represented in the original population with those represented in the founding population (i.e. the red allele might have been 50% in the founding group while it was only 16% in the original population). Use the table for these comparisons. Color Allele Frequency in original population Allele Freq. in founding population 5. What colors (if any) in the original population are NOT represented in the founding group? 6. When you compare the allele frequencies for each color, are they the same for the original population and the founding population? Why? (Use your notes to help you describe what s causing this change in allele frequencies). 7. Define bottleneck effect. 8. Compare Table #1 and Table #3. Compare allele frequencies for each allele represented in the original population with those alleles represented in the population after the hurricane (after the bottleneck event). Use the table for these comparisons. Color Allele Frequency in original population Allele Frequency after bottleneck 9. When you compare the allele frequencies for each color, are they the same for the original population and the surviving population? Why? 10. Is there more of a dramatic change in allele frequencies when alleles change in larger populations or when alleles change in smaller populations? Explain? 11. Let s assume that the Skittles are praying mantises (green bugs). A group of mantises have gone on strike and moved to a new environment, which consists of lots of greenery with many bright red flowers. Birds love to eat praying mantises. a. Which colors in the founding population would have a high fitness level in this new environment? Why? b. What might happen to those alleles in the population (increase or decrease)? c. Which colors in the founding population would have a lower fitness level in this new environment? Why? d. What might happen to those alleles in the population (increase or decrease)? e. Is natural selection acting on this founding population?

3 12. From the list below indicate whether it will lead to a founder effect or a bottleneck effect. Explain. a. Disease b. Immigration c. Storm d. Searching for food 13. Calculate the percent change of all allele frequencies after each event (founding effect and bottleneck) using the following formula: % change = allele frequency after bottleneck allele frequency of initial population x100 allele frequency of initial population Color % change after bottleneck % change after founder effect 14. In the back of your data table create 2 bar graphs (one for bottleneck effect and one for founder effect) of the percent change of each allele. Be sure to include a proper title, axislabels and units. 15. Compare your graphs with another group. Describe these comparisons.

4 Data Sheet Genetic Drift Lab: Founder Effect vs. Bottleneck Effect Table 1: Allele frequency in the gene pool for the initial population of Candus spectacularis Table 2: Allele frequency for the founding group Table 3: Allele frequency of the surviving population after bottleneck effect

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