Integrated Science II
Chapter 7
Corn Genetics
Name _______________________________
Period _________ Date _________________
/20
The genetics of corn have been extensive studied, both to improve our agricultural
varieties and to better understand the mechanisms of heredity. Corn plants are
diploid and produce both male and female gametes. Each kernel on the ear is a
separate offspring of a cross between a female and a male parent.
A monohybrid cross begins with experimental breeding between two parents that
breed true for different forms of a single trait. The trait you will investigate in this lab
activity is kernel color. The allele for purple kernels (B) is dominant and the allele for
yellow kernels (b) is recessive. One of the original parents (P generation) of this cross was purebred
for purple kernels and the other original parent was purebred for yellow kernels. These two purebred
corn plants were crossed and their offspring are hybrids and are the F1 generation. Two individual
corn plants from the F1 generation were crossed together and their offspring are the F2 generation.
Problem: How do the actual, observed results of a genetic corn cross compare with the predicted
outcome from this cross?
Procedure:
1. Complete a Punnett square to show the predicted outcome of a cross between a purebred for
purple kernels and a purebred for yellow kernels.
a. What are the genotypes of the P generation? ______ x ______
b. What is the genotypic ratio of the F1? ______ : ______ : ______
c. What is the phenotypic ratio of the F1? ______ : ______
2. Complete another Punnett square to show the predicted outcome of a cross between 2 of the
hybrid offspring from the F1 generation.
a. What is the genotype of the F1 generation? ______ x ______
b. What is the genotypic ratio of the F2? ______ : ______ : ______
c. What is the phenotypic ratio of the F2? ______ : ______
3. Hypothesis 1. Predict the phenotypic ratio of the F2 generation of a cross between a purebred
for purple kernels and a purebred for yellow kernels. Write your hypothesis in the ‘If, then’ format.
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4. Hypothesis 2. You will collect 3 samples of data, small (a single row of kernels on the ear),
medium (10 rows of kernels), and large (the total of all the medium samples in the whole class).
Predict which sample size will come closest to your predicted outcome for this cross. Write your
hypothesis in the ‘If, then’ format.
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5. Obtain an ear of genetics corn. The kernels on this ear represent the F2 offspring of a
monohybrid cross between a purebred for purple kernels and a purebred for yellow kernels.
6. Count the number of purple and yellow kernels in a single row. Record your results in the data
table below in the ‘small sample’ row.
7. Now count the number of purple and yellow kernels in 10 rows. Record your results in the data
table below in the ‘medium sample’ row.
8. Enter your group’s data into the class spreadsheet. After all the class data is entered, record the
class total number of purple and yellow kernels in the data table below in the ‘large sample’ row.
9. Using the data, calculate the phenotypic ration for each sample size. This can be done by
dividing both the number of purple kernels and the number of yellow kernels by the number
of yellow kernels in the sample. Round off the resulting numbers to the nearest tenth’s place.
For example, suppose in your small sample you obtained 25 purple kernels and 10 yellow
kernels. This gives you a phenotypic ratio of 2.5 : 1 (25/10 = 2.5 and 10/10 = 1).
Results:
Sample
Size
Total Number of
Number of Purple Kernels
Kernels in Sample
Number of Yellow Kernels
Phenotypic Ratio
Small
Medium
Large
Analysis and Conclusion:
1. How do your observed phenotypic ratios compare to your predicted phenotypic ratio for this cross?
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2. Which sample size produced phenotypic ratios that were closest to your predicted phenotypic
ratio?
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3. Why would the class results be more useful than just your own individual results?
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Conclusion:
1. Purpose: _____________________________________________________________________
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2. Summary Results (describe what you observed): _____________________________________
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3. Analysis (explain why this happened): ______________________________________________
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4. Closing Statement (what did you learn): ____________________________________________
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