Monohybrid Crosses
Purpose: To demonstrate how chance can affect combinations of genes and use the Punnett
square to predict the genotype and phenotype.
Procedure:
1. Obtain 2 bags for you and your partner. Make sure there are 50 red beans & 50 white
beans inside. Each bag represents a parent flower. Each bean represents an allele
for flower color. Red flower color is dominant to white.
2. Without looking inside the bags, remove 1 bean from each bag. Since each parent
contributes 1 allele at random to each offspring, you will model a cross between these
2 parents by choosing 100 random pairings. Do this by simultaneously picking one
bean from each bag without looking.
3. Place the pair of beans together on the table. The pair represents one offspring.
Record the color combination of beans (alleles) in Table 1 by putting an “X” in the
correct column.
4. Return the beans to their original bags and repeat 99 more times. Total your
results and enter your data in Table 1. Summarize this data in Table 2.
5. Enter your data in the class data table on the board. Record other groups’ data as it is
entered on the board in Table 3. Summarize this data in Table 4.
6. Fill out the Punnett square below showing the cross of the parent bags & the possible
offspring produced.
Genotypes:
Phenotypes:
Table 2: Offspring Totals
Genotype
Homozygous dominant (RR)
Genotype Total
Heterozygous (Rr)
Homozygous recessive (rr)
Phenotype
Phenotype Total
Red Flower
White Flower
What percentage of offspring were red? _________________
What percentage of offspring were white? ________________
*NOTE: Attach Table 3: Offspring Numbers (Entire Class) to this packet
Table 4: Offspring Totals (Entire class)
Genotype
Homozygous dominant (RR)
Genotype Total
Heterozygous (Rr)
Homozygous recessive (rr)
Phenotype
Phenotype Total
Red Flower
White Flower
ANALYSIS QUESTIONS
1. What are the genotypes & phenotypes of the parents?
2. What does each bean represent?
3. When the beans were selected & paired, what did the pairs of beans represent?
4. Describe the genotypes of both parents using the word(s) homozygous or heterozygous.
5. What trait is being studied in this investigation?
6. How did your results compare with the predicted results of 25% homozygous dominant
(RR), 50% heterozygous (Rr), & 25% homozygous recessive (rr)?
7. How could you get the predicted results to be closer to the actual results?
8. How does chance affect allele combination?
Table 3: Offspring Numbers (Entire class)
Group Number
Homo. Dom. (RR)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Hetero. (Rr)
Homo. Rec. (rr)