Name
Class
Date
Backwards Genetics
An A-Maize-ing Investigation (corny, I know)
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
that fertilized the egg. The fertilized egg then grew into corn kernels (seeds). Each kernel is an
offspring. The colored layer of the seed that is visible is a part of the endosperm. If the endosperm is
not pigmented (colorless), the yellow color of the inner tissue will show through making it appear
yellow or creamy colored. If it is pigmented it will appear purple.
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, and
wrinkle when dried. Thus the kernels (offspring) can be purple and smooth,
purple and wrinkled, yellow and smooth, or yellow and wrinkled.
Seed Color Gene
Procedure:
R = purple color
r = yellow color
1.
Obtain four ears of corn with unknown parent genotypes.
2.
Count and record the number of each of the phenotypes on the ears of
corn.
3.
Calculate the phenotypic ratio (in percentages).
4.
Determine the genotypes of the parents by creating Punnett Squares.
Show your work on your own paper and attach it to this one when you
turn this in. No work = no credit. If you do not figure out the parents’
genotype after creating three Punnett squares, move on to the next
problem and save your work.
Seed Texture Gene
S = smooth texture
s = wrinkled texture
Corn EXAMPLE – One gene
Data Collection:
Phenotype
Number of Kernels
Observed
Percentage of Kernels
Observed
Smooth
169
169/(169+55) = 75%
Wrinkled
55
55/(169+55) = 25%
Final Answer
Parent #1
Percentage of Kernels Expected
from Punnett Square
Parent #2
Genotype
Phenotype
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In order to fill out the “Percentage of Kernels Expected from Punnett Square” column, you need to
construct a Punnett square to calculate the percentage of kernels expected, and then compare to
what you actually observed. Remember, most likely the observed data will not exactly match your
expected results from your Punnett square, but is within 1-2% of the expected.
Corn A – One gene
Data Collection
Phenotype
Number of Kernels
Observed
Percentage of Kernels
Observed
Percentage of Kernels Expected
from Punnett Square
Purple
Yellow
Final Answer
Parent #1
Parent #2
Genotype
Phenotype
Corn B – One gene
Data Collection
Phenotype
Number of Kernels
Observed
Percentage of Kernels
Observed
Percentage of Kernels Expected
from Punnett Square
Purple
Yellow
Final Answer
Parent #1
Parent #2
Genotype
Phenotype
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Corn C – Two genes
Data Collection
Phenotype
Number of Kernels
Observed
Percentage of Kernels
Observed
Percentage of Kernels Expected
from Punnett Square
Purple / Smooth
Purple / Wrinkled
Yellow / Smooth
Yellow / Wrinkled
Final Answer
Parent #1
Genotype
RrSs
Phenotype
Purple / Smooth
Parent #2
Corn D – Two genes
Data Collection
Phenotype
Number of Kernels
Observed
Percentage of Kernels
Observed
Percentage of Kernels Expected
from Punnett Square
Purple / Smooth
Purple / Wrinkled
Yellow / Smooth
Yellow / Wrinkled
Final Answer
Parent #1
Genotype
ppss
Phenotype
Yellow / Wrinkled
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Parent #2
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Conclusion
Answer the following question in complete sentences.
1.
Describe how you think what we learned about in the genetics unit is important to you outside
of school? How can it be used?
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