Name: ___________________________
GENETICS AND PROBABILITY: “THE BEAN LAB”
How does chance affect combinations of genes?
Purpose: Mendel predicted the outcomes when crossing pea plants by using experimental data. In this
experiment, you will model his experiments and results. Keep in mind that Mendel actually grew the plants
from seed and had to wait until they were able to reproduce to cross them, and then he had to wait for the
offspring to flower before he knew his results. Because Mendel did all the hard work and we now understand
the laws of genetics and dominant and recessive genes, you get to run the experiment in a much faster way.
You will be crossing two parents who are both heterozygous for daisy color, representing Mendel’s F1
generation. The offspring in your results will represent Mendel’s F2 generation.
Materials: 2 paper bags, 100 red beans, 100 white beans, calculator
Procedure:
1) Use a Punnet square to predict the outcome of a cross between two heterozygous daisy plants. The
dominant allele is yellow flower color (Y) and the recessive allele is pink flower color (y).
2) In table 2 below, write your predictions for the percent of daisies that will be homozygous for yellow
flower color, homozygous for pink flower color, and heterozygous (phenotype yellow flower color) if
100 offspring are observed. Make a prediction for your group and for the class as a whole.
3) Place 50 red beans and 50 white beans into a paper bag. Label it “female”. Repeat for a second bag and
label that bag “male”. Each bean represents a possible allele for flower color. The white beans
represent the allele for yellow flowers (Y). The red beans represent the allele pink flowers (y).
4) Without looking, remove one bean from each bag. The bean pulled from each bag represents the allele
for flower color donated to the offspring by that parent. Put a tally mark in the appropriate box in table
1, indicating which phenotype/genotype you pulled. Then put each bean back in its original bag.
5) Repeat this 99 times.
6) Add up your tally marks and record the total numbers in data table 1. Also, write your data on the board
as part of the classroom chart.
7) Record total numbers for the entire class in table 1.
Table 1: Talley representing the genotypes and phenotypes of 100 daisy offspring.
Homozygous yellow (YY)
Heterozygous yellow (Yy)
Homozygous pink (yy)
Tally
Total
Number—
Your
Group
Total
Number-Class
Table 2: Predicted and actual percent of daisies of each phenotype in 100 offspring.
Predicted
Actual
Predicted
Actual
Predicted
Actual
homozygous homozygous heterozygous heterozygous homozygous homozygous
yellow
yellow
yellow
yellow
pink
pink
Your group’s
total (percent)
Class total
(percent)
Analysis:
1) What percentage of your group’s offspring were purebred (homozygous) yellow? SHOW YOUR
WORK! Round to the nearest tenth of a percent. Use the following formula:
% of homozygous yellow offspring = (# of homozygous yellow offspring/ Total # of observed offspring) x 100
Record this number in the table 2.
2) What percentage of your group’s offspring were heterozygous yellow? SHOW YOUR WORK! Round
to the nearest tenth of a percent. Use the following formula:
% of heterozygous yellow offspring = (# of heterozygous yellow offspring/ Total # of observed offspring) x 100
Record this number in table 2.
3) What percentage of your group’s offspring were purebred (homozygous) pink? SHOW YOUR WORK!
Round to the nearest tenth of a percent. Use the following formula:
% of homozygous pink offspring = (# of homozygous pink offspring/ Total # of observed offspring) x 100
Record this number in table 2.
4) Repeat the above steps for the class data. SHOW YOUR WORK BELOW! When complete, record
these numbers in the data table.
Homozygous yellow:
Heterozygous yellow:
Homozygous pink:
Conclusion:
1) Which combination occurred most often? What phenotype does this combination represent?
2) Write your results in ratio form, (___: ___:___)with the homozygous dominant total percent as the first
number, the heterozygous result as the second number, and the homozygous recessive result as the last number.
Do the same for the class data.
My group’s ratio:
Class ratio:
3) How do the expected and observed results for your group differ?
How do the expected and observed results for the class differ?
What observations can you make about the number of samples and the observed results (class vs. group data)?
4) Does chance affect allele combination? Explain your answer.
5) How might you get your actual results to be closer to your predicted results?
6) How did your experiment compare with Mendel’s experiments in terms of time taken and quality of your
hypothesis?