Biology
Dihybrid Cross Lab
Names____________________________________
Per_______________
To figure out probability of certain chance occurrences—such as the chance of one organism receiving a
specific allele vs another—requires multiple trials. In life, however, we usually cannot simply make
multiple organisms just to see what the probability is. Instead, we will use a model. You and your
partner will model a dihybrid cross using pastas and cups.
Materials (Per Groups)
8 Cups
2 Red Pasta
2 Green Pasta
2 Round Pasta
2 Curled Pasta
2-4 Textbooks (or any other object to form a wall)
This lab sheet
Procedure
1. You will be testing the possible offspring genotypes that come from two parents who are
heterozygous for both the shape and the color traits. Prior to this you will need to perform a
Punnett Square to establish what genotypes you EXPECT to appear.
Trait
Color
Shape
Parent #1: GgTt
Genotypic Ratios
Dominant Allele
Green ( G)
Tube ( T )
Recessive Allele
Red (g )
Curled ( t )
Parent #2: GgTt
Phenotypic Ratios
2. Find a partner and collect all necessary materials. Each partner needs 4 cups and 1 of each type
of pasta.
3. Each partner turns their cups upside down and writes “Color” on the bottom of two cups. Write
“Shape” on the bottom of the other two cups.
4. Set up a wall with textbooks or some other object. The barrier should hide cups from each
partner but still allow room to move cups back and forth across the table.
5. From behind the protection of the barrier, each partner places the red pasta under one cup
marked “color” and the green pasta under the other cup marked “color.”
6. From behind the protection of the barrier, each partner places the round pasta under one cup
marked “shape” and the curled pasta under the other cup marked “shape.”
7. On the graph marked “Figure 1” write each partner’s name on one of the axes.
a. In the shaded spaces under your name are written the four possible allele combinations
that can be made with your two genes. The genes, alleles, and their
dominance/recessiveness are also included.
8. Each partner hides their pasta pieces under their cup and moves them to the center of the table.
9. Each partner will then randomly choose one cup marked “shape” and one cup marked “color”
from the other partner’s cups. DO NOT LOOK UNDER THE CUPS BEFORE CHOOSING.
10. Lift the cups to reveal which color and which shape was selected. Place a tally mark in one of the
16 grid spaces in the table according to which gamete combination was chosen for each parent.
a. Example: Partner one’s combination of color and shape was “Green and Tube.” Locate
the column marked “GT”
b. Then, Partner two’s combination of color and shape was “Red and Curled.” Locate the
row marked “gt”.
c. Find the square grid where this column and this row intersect. Mark a tally in this
square.
11. Cover the pastas and drag the cups back behind the barrier. While keeping the cups hidden
behind the barrier, mix up the cups and/or which pasta is under which cup. **MAKE SURE THE
PASTA UNDER THE CUP FITS WITH THE TRAIT WRITTEN ON THE CUP**
12. Drag the cups back into the center of the table. Repeat steps 8-10, randomly choosing alleles
from your partner’s options. Place a tally into the appropriate section of figure 1 according to
which combination of alleles was picked for each partner.
13. Repeat steps 8-12 until you have a total of 64 tallies placed on the squares in figure 1.
Figure 1
Name_____________________________________
Name______________________________________________________
Possible Allele
Combinations
GT
Gt
gT
GT
Gt
gT
gt
Trait
Dominant Allele
Recessive Allele
Color
Shape
Green ( C)
Tube ( T )
Red ( c )
Curled ( t )
gt
Post Lab
1. What is the genotypic ratio of your offspring?
2. What is the phenotypic ratio of your offspring?
3. Did you get the exact ratio you predicted? Why or why not? What caused this to happen?
4. What do the cups represent in this experiment?
5. Estimate what you would expect to be the ratios of this dihybrid cross if you were to repeat this
experiment 500 times? Why?
6. If a mutation occurs tomorrow in the pasta population and “green” color suddenly becomes
deadly, what do you think will be the most common phenotype in 100 years? Why?
7. Create a graph showing the number of organisms that showed the each phenotypic combination
(There should be four total).