Teosinte Case Study
GPS: S7L5. Students will examine the
evolution of living organisms through inherited
characteristics that promote survival of
organisms and the survival of successive
generations of their offspring.
Riddle: What do coca-cola, baby diapers,
fireworks, bubble-gum, bio-diesel, and
glue have in common?
Answer: They all have corn, or a corn byproduct as an ingredient!
Just so you know…
King Corn:
http://www.youtube.com/watch?v=nvMxIE
gbsIo&wide=1
Start at min. 3:03 – 4:30
Corn’s Mysterious Ancestor
• For years scientists were baffled about
corn’s wild ancestor. While other grain’s
parents were easily identifiable in the wild,
corn’s genetic predecessors remained a
mystery.
Corn vs. Teosinte
•
Scientists finally followed the genetic trail
back to teosinte, a wild grass, and
discovered that there were only a few
major differences in their gene code.
Can you spot the differences?
Branching
Teosinte branches, which
allows for more ears per
plant. Maize does not, and
all that extra energy goes
into producing larger ears
of corn.
Ear Structure
• Teosinte has 2 rows of
seeds
• Corn has 8-12 rows of
seeds
Seed Structure
• Teosinte seeds
(kernels) are covered
by a fruitcase
•In corn, the fruitcase is
part of the corn cob,
leaving the corn
kernels accessible
Why did this happen?
Take a minute to brainstorm what could
have caused these changes, and what
could have made them so widespread
Why did this happen?
• First, genetic mutations occurred naturally in
teosinte
• Native Americans found those mutations were
helpful to them (IMPORTANT: why were
branching, ear structure, and seed structure
beneficial?).
• They saved seed from these better teosinte
plants, and planted more and more each year.
• Eventually these plants no longer looked like
teosinte, and became a new plant…maize.
Artificial Selection
• Human intervention in animal or plant
reproduction to ensure that certain desirable traits
are represented in successive generations.
http://www.answers.com/topic/artificialselection#ixzz2aLLKKeDP
• For corn, those “desirable traits” were larger ears
(because of branching and continued selecting for
large ears), more kernels per ear (because of
ear structure), and more accessible
seeds/kernels (because of the seed structure
and reduced fruitcase)
Artificial Selection
• http://learn.genetics.utah.edu/content/varia
tion/artificial/
Genetic Diversity of Maize
• Over thousands of years, corn grew in genetic
diversity. Native Americans may have selected
for corn that grew well in a certain region, that
was good for making tortillas, or another that
was good for making tamales. Modern people
have selected for sweet corn, like the kind you
eat on the cob.
Corn Today
• Today, most farmers
grow dent corn (a field
corn which is not
sweet). It is used to
feed livestock, poultry,
and is easily converted
to high fructose corn
syrup and corn starch.
In the garden
• Crops, Livestock, and pets have all undergone
the process of artificial selection.
• Humans have interfered
to make fruits and
vegetables larger,
sweeter, different shapes
and colors, and generally
better suited for our use!