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Name __________________________
Per _________
Lab: Genetic Drift
Title: Genetic Drift of Bead Organisms on Two Different Islands
Background: Genetic drift is the change in allele frequency due to random events.
Natural selection is a non-random change in biological traits in which individuals that
are better adapted to their environment survive. There are a couple of types of genetic
drift. The first type is bottleneck. This is when a disaster (earthquake, floods, fires,
predation, etc.) results in only a small population surviving that doesn’t represent the genetic diversity of the original
population. An example of this would be our Cheetah population. The second type of genetic drift is the Founder effect.
This is when a small group of individuals from a large population colonize a new area, which also reduces genetic
variation. An example of this would be Darwin’s finches on the Galapagos Islands.
Small population sizes are more strongly influenced by genetic drift than large populations. This means that the genetic
frequencies of alleles in small populations are more likely to vary from one generation to the next from the original
population. Often, genetic variation is rapidly lost in small populations and random events can create rapid genetic
Problem: How will genetic drift affect the diversity among the bead organisms in a small population on a small island vs. a
larger bead organism population on a large island?
Hypothesis: (Don’t forget to use “If…then…because” format)
 Big Island Bowl and Little Island Bowl
 Bead Organisms: Pink, Red, White, Orange and Yellow
Large Island
1. The large island will start with a total population of 50 individuals
2. Place ten (10) beads of each color into the Big Island Bowl (Total = 50 beads). Record in year 1
3. With your eyes closed (remember that genetic drift is random, not like natural selection), pick 25 unlucky members
from the Big Island (50% of the population) to randomly die.
4. Put the beads organisms that you picked back in the “gene pool.” All the beads left on the island are going to
5. Let each surviving bead organism on your island reproduce one individual identical to it and place those into the
island bowl.
6. Record the new number of each color of bead in your data table under "Year 2". Your large island population must
be 50 beads at the end of each generation.
7. Continue this procedure for three (3) more years (for a total of 5 years).
Small Island
8. The small island will start with a total population of 10 individuals
9. Place two (2) beads of each color into the Small Island Bowl (Total = 10 beads). Record in year 1
10. Repeat steps 3-7, making sure to select only 5 each to die
11. Record your data in your data table.
Data Table
Small Island
Big Island
Color Allele
Year 1
Year 2
Year 3
Year 4
Year 5
Graph your data on the attached graph paper (Remember your TAILS!!!!! Title, Axes, intervals, Label, Scale)
Analysis Questions
1. This graph should be a line graph not a bar graph.
a. When do we use bar graphs?
b. When do we use line graphs?
2. What is the independent variable and which axes does it go on?
a. Range
b. Scale
3. What is the dependent variable and which axes does it go on?
a. Range
b. Scale
4. Describe how the proportion of alleles (for bead organism colors) changed over time on the small island.
5. Describe how the proportion of alleles (for bead organism colors) changed over time on the big island.
6. Explain why the proportion of alleles changed more on one of the islands than on the other?
7. Did any alleles go extinct on either of the islands? List which ones
8. Look at your graphs, which graph has the most bead organisms species that survived?
9. Do you think that losing alleles will helps or hurts populations? Explain why.
10. Can you propose any ways that an island could get extinct alleles back into its gene pool?
11. Natural Selection & Genetic Drift both cause populations to evolve over time. Explain how they're different.
12. Imagine that the colored beads were dominant to the white beads. Calculate the allele frequency if 20 were
homozygous dominant, 20 were heterozygous for the “color”, and 10 were homozygous recessive. What is the allele
frequency of the recessives? Show your math work!!!
13. Tell me whether you accept or reject your hypothesis, and explain why.