Lab: Mouse Genetics (two traits)
Purpose: Explore the law of independent assortment by examining a dihybrid cross in mice.
Question: What is the effect of the inheritance of one trait on the inheritance of a second trait?
Hypothesis: If a mouse inherits a particular form of one trait, then the inheritance of the other
trait will not be affected because alleles assort independently.
Variables:
Independent variable: inheritance of the first trait
Dependent variable: inheritance of the second trait
Data:
Step 1: Predict the offspring for a cross of true-breeding lineage (BBEE x bbee)
Black fur and
black eyes
Predicted
Fraction
Predicted
Percentage
Black fur and
red eyes
White fur and
black eyes
White fur and
red eyes
16/16
0/16
0/16
0/16
100%
0%
0%
0%
Step 2: Simulate the cross in step 1 and compare the predicted values to simulated values
Predicted
Fraction
Predicted
Percentage
Simulated
Fraction
Simulated
Percentage
Black fur and
black eyes
Black fur and
red eyes
White fur and
black eyes
White fur and
red eyes
16/16
0/16
0/16
0/16
100%
0%
0%
0%
10
0
0
0
100%
0%
0%
0%
Step 3: Predict the offspring of a dihybrid cross (BbEe x BbEe)
Predicted
Fraction
Predicted
Percentage
Black fur and
black eyes
Black fur and
red eyes
White fur and
black eyes
White fur and
red eyes
9/16
3/16
3/16
1/16
56.25%
18.75%
18.75%
6.25%
Step 4: Simulate the cross in step 3 and compare the predicted values to simulated values
Black fur and
black eyes
Black fur and
red eyes
White fur and
black eyes
White fur and
red eyes
9/16
3/16
3/16
1/16
Predicted
Percentage
56.25%
18.75%
18.75%
6.25%
Simulated
Fraction
5/10
2/10
2/10
1/10
Simulated
Percentage
50%
20%
20%
10%
Predicted
Fraction
Conclusion:
If a mouse inherits a particular form of one trait, then the inheritance of the other trait will not
be affected because alleles assort independently. The hypothesis wouldn't have been supported
by the data if the traits of white fur and red eyes were always inherited together. These
differences most likely result from expected randomness.