Evolution Revised January 2018
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DATE
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Popped Secret:
The Mysterious Origin of Corn
Short Film
Student Handout
NAME_______________________ _________________
This handout supplements the short film Popped Secret: The Mysterious Origin of Corn.
1. Which of the following statements describes domestication?
a. It is the process by which animals are trained to do tricks useful for human needs.
b. It is the process by which wild species have been turned into species with traits that are useful for
human needs.
c. It is the process by which animals build nests to attract mates and raise young.
d. It is the process by which plants have evolved to fill in ecological niches over time.
2. To illustrate how common corn is in a typical American diet, the film narrator gives many examples, from
corn-on-the-cob to foods that contain cornstarch and corn syrup. The narrator also mentions meat. What is
the connection between the meat we eat and corn?
3. Dr. Beadle concluded that teosinte was the likely ancestor of maize. On what evidence did he base this
conclusion? Select all that apply.
a. Teosinte looks like maize.
b. Teosinte and maize have nearly identical chromosomes.
c. A cross between teosinte and maize produces fertile hybrid offspring.
d. Christopher Columbus discovered written records of maize’s domestication from teosinte.
4. a. Fill in the table below to compare teosinte and maize.
Extent of branching
Number of rows of
kernels per cob
Kernel type (naked or
enclosed in a hard fruitcase)
Teosinte
Maize
b. Pick one of the characteristics of maize from the table and explain how it makes the crop more useful to
humans than teosinte?
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Short Film
Popped Secret: The Mysterious Origin of Corn
Student Handout
5. Dr. Beadle conducted an experiment to determine how many genes control the differences between maize
and teosinte. He crossed teosinte with maize (the two parental plants) to produce F
1
hybirds, and then
crossed the F
1
plants to produce an F
2
generation (offspring). He then looked at the appearance, or
phenotype of the offspring. Based on classical genetics, he predicted if just one gene was responsible for all
the differences between maize and teosinte, a parental phenotype was expected in one of every four
offspringin other words ¼ of the offspring would look like maize and ¼ would look like teosinte. If two
genes are involved, one out of every 16 offspring would look like maize and one out of 16 like teosinte. This
relationship can be summarized by this equation: X = (¼)
n
a. In the equation above, X represents the proportion of offspring expected to have a parental phenotype.
What does n represent?
b. Dr. Beadle planted 50,000 plants and discovered that 1 out of 500 offspring had the phenotype of one
parent and 1 out of 500 of the other parent. Approximately how many plants had a teosinte phenotype?
A maize phenotype? What phenotype(s) did the rest of the plants have?
c. Use the equation X = (¼)
n
to explain how Dr. Beadle came to conclude that four or five genes are
responsible for the differences between maize and teosinte.
d. Explain how changes in a small number of genes can result in very different-looking plants.
6. The film describes two independent sources of evidence that have been used to estimate when maize was
first domesticated: genetic evidence and archaeological evidence. Do these two sources of evidence support
each other? Explain your answer.
7. To demonstrate how two different genes can explain the different traits in teosinte and maize, Dr. Doebley
and colleagues used careful breeding to transplant each gene from one type of plant to the other. In the
table below, draw and/or describe the results of each cross and explain what you can infer about the
function of the genes.
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Short Film
Popped Secret: The Mysterious Origin of Corn
Student Handout
Gene
Moved from
Draw the result
What can you infer about
the function of the gene?
Teosinte
Maize
fruitcase
gene
Maize
Teosinte
Teosinte
Maize
branching
gene
Maize
Teosinte
8. Humans have been selecting maize for desirable characteristics ever since domestication of the crop began.
Figure 1 below describes the traits of maize cobs found in four archaeological deposits from the Tehuacán
cave in Puebla, Mexico. Rachis diameter refers to the diameter of the cob at its base. Average number of
rows refers to the number of rows of kernels per cob.
a. Which archaeological layer contains the oldest maize remains? The youngest?
b. Use data to compare and contrast the oldest and youngest maize cobs in the archaeological record.
Short Film
Popped Secret: The Mysterious Origin of Corn
Student Handout
Figure 1. Corn cob fossils
discovered in different
layers of the Tehuacán cave
in Mexico. The age of each
layer is indicated. Present-
day corn consists of two
different varieties. For each
corn sample, the average
rachis diameter and row
number are noted.
c. The authors compared the ancient maize in the archeological record to two different modern maize
varieties: arrocillo and tabloncillo. How do these two varieties compare to the cobs found in the
archeological record? Why do you think the authors selected these two varieties to use for their
comparisons?
d. Based on these data, what can you say about the kinds of traits that farmers have been selecting for in
maize over the past 5,000 years?
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