Name _________________________________
Partner ________________________________
Date ______________________
Corn Genetics – PreAP Biology
Adapted from Bio Fax by Flinn Scientific
Background
Period ______
As we all know, yellow corn kernels are a common color. Purple corn kernels are not nearly as common! The study of corn kernel color illustrates some basic genetic principles including
Each corn kernel on an ear of corn is a separate offspring resulting from a cross between a female parent (of which the ear and the corn cob are a part) and a male parent, which supplied the pollen grains that fertilized the egg.
The fertilized egg then grew into the corn kernels (seeds). The colored layer of the seed that is visible is a part of the endosperm. If the endosperm is colored, it is observable. If the endosperm is not pigmented (colorless), the yellow color of the inner tissue shows through, and the color appears as yellow, white or cream.
In addition to color, kernels also display another easily observable trait. Those kernels that are starchy inside remain smooth when dried. Those kernels that contain sugar and are sweet, wrinkle when dried. Thus the kernels
(offspring) can be purple and smooth, purple and wrinkled, yellow and smooth, or yellow and wrinkled. (Please consult a basic biology text for further details about the structure of a corn seed and the life cycle that produces seeds in plants.)
In producing the ears of corn used in this laboratory, the plant breeder started by selecting plants that were pure-breeding, i.e., ones whose offspring always produced purple, smooth kernels and another whose offspring always produced cream-colored, wrinkled kernels. The pollen from one of these strains was placed on the corn silks of the other strain. The seeds were then produced and represent the first generation of corn seeds. The genetic cross can be diagrammed as follows:
Parents (P): RRSS X rrss
(pure breeding purple and smooth) (pure breeding non-purple and wrinkled)
R = purple gene r = non-purple gene (cream)
S = starchy gene (smooth)
First generation (F1): RrSs
(all offspring purple and smooth) s = sweet gene (wrinkled)
The plant breeder next made two kinds of crosses that produced the ears of corn used in this laboratory. The first cross involved crossing two of the first generation offspring (RrSs X RrSs). The second cross (often called a back cross) involved crossing a first generation offspring with one of the original non-purple offspring (RrSs X rrss).
PreLab Assignment
1.
Define the following terms: dominant - recessive - dihybrid cross - phenotype - genotype - independent segregation –
2.
Why does counting corn kernels equate to counting offspring?

3.
What is the endosperm?
4.
Which two carbohydrates result in the round and wrinkled appearance of the kernels?
5.
Predict the phenotypic ratios that will result from each of the crosses described to produce F2 offspring using a
Punnett square. Record the information in PreLab Data Table 1A & 1B. Title the table.
Punnett Square for Cross A: RrSs X RrSs
Genotypes
PreLab Data Table 1A. Predicted Results of Cross A
Phenotypes Number of Kernels/16
Purple/smooth
Purple/wrinkled
Non-purple/smooth
Non-purple/wrinkled
Phenotypic Ratio for Cross A: _____________________________________
Punnett Square for Cross B: RrSs X rrss
Genotypes
PreLab Data Table 1B. Results of Cross B
Phenotypes Number of Kernels/16
Purple/smooth
Purple/wrinkled
Non-purple/smooth
Non-purple/wrinkled
Phenotypic Ratio for Cross B: ______________________________

Materials
Ear of genetic corn wrapped in plastic
Vis-à-vis pen
Paper towel
Warnings
 Do NOT remove the plastic wrap from the corn!!!
 Do NOT get the outside of the corn WET!!!
 Wipe the dot from the vis-à-vis pen off with a barely damp paper towel at the end of the lab
 Do not count loudly; use a 3-inch voice or count in your head
Procedure
With your partner, look at the ear of corn at your lab station. Write a hypothesis for your ear of corn (Ear 1) predicting what the parental genotypes were that created the pattern of colors you see. Now, look at the ear of corn that the other group has across from you at the lab station. Write a hypothesis for their ear of corn (Ear 2), predicting what the parental genotypes were that created the pattern of colors you see.
Analyze your Ear 1. Using a vis-à-vis pen (so it will come off!) mark first kernel of the row you are starting with.
Do NOT mark each kernel as you count. One of you will be the counter of kernels, the other will be the recorder of data. The counter should count all of the purple/smooth in that row and tell the recorder that number. The recorder will then record that number in the purple/smooth No. of Kernels per row box. The counter will count ON THAT SAME ROW the number of purple/wrinkled and give the recorder that number. The counter will continue counting the number of non-purple/smooth, then non-purple/wrinkled for that SAME ROW. Once that row is complete, the counter will mark the next row and repeat the same counting/recording procedure until all kernels in each row are counted and recorded.
Total each of your phenotypes and record the total number of kernels of each phenotype counted. Record these in the first data table. Wipe off the vis-à-vis mark with a slightly damp paper towel. Do NOT put the corn under the running water or leave wetness on the plastic of the corn.
For Data Table 2, obtain the data for Ear 2 from the other group working at your lab station and record it in Data
Table 2. Give that group your data from your Ear 1 and they will record your data as their Ear 2 data.
Each lab station should be dry and clean with 1 ear of corn, 1 vis-à-vis (with cap on), and 1 dry paper towel so it will be ready for the next class. If your class is the last of the day, please listen to your teacher for clean up instructions.
Hypothesis
Ear 1: __________________________________________________________________________________________
________________________________________________________________________________________________
Ear 2: __________________________________________________________________________________________
________________________________________________________________________________________________
Data
Phenotypes
Data Table 1. Phenotypic Counts of Ear 1
Number of Kernels per Row TOTAL Number of Kernels on Ear
Purple/smooth
Purple/wrinkled
Non-purple/smooth
Non-purple/wrinkled

Phenotypes
Purple/smooth
Purple/wrinkled
Data Table 2. Phenotypic Counts of Ear 2
Tally Marks Number of Kernels
Non-purple/smooth
Non-purple/wrinkled
Analysis
1.
Using the Number of Kernels data from Table 1, divide each number by the smallest number counted. Show your work in the space below:
Ex) Number of kernels observed = 115, 41, 38, 14
14/14 = 1
Table 1:
Now repeat for Table 2:
38/14 = 2.43 41/14 = 2.92 115/14 = 8.21
2.
Look at the answers you got in problem 1. Which of the two
phenotypic ratios does it most closely match? (in the example above, you would write 9:3:3:1, NOT 8:3:2:1 or 8.21:2.92:2.43:1)
Write the phenotypic ratio you
in ear 1: _________________________
Write the phenotypic ratio you
in ear 2: _________________________
Conclusion
1.
Based on the phenotypic ratios you observed, what were the parent genotypes that resulted in each of the ears of corn (look back at the background)?
Parent genotypes for ear 1: __________________ X ___________________
Parent genotypes for ear 2: __________________ X ___________________
2.
Was your hypothesis supported by the data? _______________ Why or why not?
3.
The data is not perfect (you did not get exactly the expected numbers in your observed data). Do you think this difference in the data is important/significant, or that it just occurred by chance? __________________________
Why?
*You can statistically analyze the data. There are several calculations that can be done. One of these is called chi-square test. You will learn how to do this calculation if you take AP Biology  It will tell you the probability that it occurred by chance and allow you to make a mathematical conclusion about importance/significance of any deviation from the expected results.