Name__________________________
The Effect of Natural Selection on Rock Pocket Mouse Populations
View the video “Making of the Fittest: Natural selection and Adaptation” http://www.hhmi.org/biointeractive/making-fittest-natural-selection-and-adaptation
1. In what 2 different environments are rock pocket mice found?
2. What are the 2 variations of rock pocket mice? How are these variations
genetically based? Which variety is caused by a mutation?
3. What is the main reason why some rock pocket mice survive better than others?
In this experiment, we will be simulating the natural selection of different varieties of
rock pocket mice. We will test to see what happens to the genetic make-up of a
population when the survivability rates of different varieties of mice are affected.

Independent variable: _________________________________
o Control group: _________________________________
o Experimental group: _____________________________

Dependent variable: Allele frequency
Explain how we calculate allele frequency:

Hypothesis:
Key for this lab:
 Red bead (R) = ___________ fur
 Blue bead (r) = ___________ fur
Genotypes
RR or Rr
rr
Phenotypes
Procedure – Control Group
1. Obtain 3 cups. The cup is the “Parental”, the other cup is “Offspring”, and the
third cup is the “Morgue”.
2. Place 80 red beads and 80 blue beads in the “parental” cup. Make sure the bead
are well mixed (stir them).
3. Assume the genotype ratio for the parent population is 20 RR, 40 Rr, 20 rr.
4. Without looking, reach in the parental-cup and remove 2 beads. This represents
the genotype of the offspring. Record the offspring’s genotype and phenotype in
your lab notebook. After recording, place the offspring in the “offspring” cup.
5. Without looking, reach in the parental-cup and remove 2 beads. This represents
the genotype of the offspring. Record the offspring’s genotype and phenotype in
your lab notebook. Repeat this 19 more times, so you have data for 20
offspring.
6. Record the allele frequencies for this generation on table 1.
7. Return the offspring beads to the parental cup. Repeat for a total of 3
generations, recording the allele frequencies for each generation.
Procedure – Experimental Group
In this part, we are assuming that the mice are living in the rocky environment and
therefore will be camouflaged better if they have dark fur. So, any offspring that is “RR
or Rr” will have a greater chance of being preyed upon.
1. Return all 160 beads (80 red and 80 blue) into the cup labeled “parental”.
2. Without looking, reach in the parental-cup and remove 2 beads. This represents
the genotype of the offspring. Record the offspring’s genotype and phenotype in
your lab notebook.
a. If the genotype is RR or Rr, you will roll a die. If an even number is rolled,
the mouse lives. If an odd number is rolled, the mouse gets caught by a
predator and dies. If the mouse lives, it goes in the “offspring” cup. If the
mouse dies, it goes in the “morgue” cup.
b. If the genotype is rr, you will roll a die. If 2 through 6 is rolled, the mouse
lives and and goes into the “offspring” cup. If a 1 is rolled, the mouse dies
and goes into the “morgue” cup.
c. Repeat this 29 more times, so you have data for 30 offspring.
3. Record the % of R and the % r for each generation on the table 2.
4. Return the beads from the “offspring” cup and place them in the “parental” cup.
Leave the beads that you put in the “morgue” cup in the “morgue” cup.
5. Start over for a new generation, collecting 30 offspring from the parental cup. Do
this same thing for 3 more generations so a total of 5 generations are collected.
6. After the completion of all 5 generations, collect the allele frequencies for each
generation on Table 2.
AP Biology – Population Genetics
Results:
Name______________________
Table 1: Control Group data
Prediction: If there is no selection for either allele, the allele frequency should...
___________________________________________________________________
Generation
0
50 (group)
%R*
50 (class)
50 (group)
%r
50 (class)
1
2
3
*%R = Total “R” divided by Total R + r
Table 2: Experimental Group data
Prediction: If there is selection for the “r” allele, the allele frequency should….
Generation
0
%R*
50 (group) 50 (class)
%r
50 (group) 50 (class)
1
2
3
4
5
Create 2 line graphs (x-y scatter) of the class data, with the allele frequency (% allele)
on the Y axis and the generation (round) on the X-axis. Have 2 separate lines for each
allele (R or r). Use Excel and use SEM as error bars.
Graphs need to have a descriptive title and labels for axes. Have a legend identifying
which allele is which line. Each graph needs to have a caption that describes the trends
seen on the graph. Remove this page of the packet. Print out graphs and attach them
to this page.
Analysis
1. Examine the first graph. Did the allele frequencies remain constant as expected
by our hypothesis? If not, what caused the allele frequencies to change?
2. What is genetic drift? How does the first graph demonstrate genetic drift?
3. Compare the slope of the “R” allele in the first graph (control) with the slope of
the “R” allele in the second graph (experimental).
4. What caused there to be the difference in slope between these 2 graphs (what
cause were we simulating)?
5. Based on our definition of evolution, how does this lab demonstrate evolution?