Teosinte Case Study

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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.

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• Riddle What do coca-cola, baby diapers,
  fireworks, bubble-gum, bio-diesel, and glue have
  in common?

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• Answer They all have corn, or a corn by-product
  as an ingredient!

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Just so you know

• King Corn http//www.youtube.com/watch?vnvMxIEgb
  sIowide1
• Start at min. 303 430

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Corns Mysterious Ancestor

• For years scientists were baffled about corns
  wild ancestor. While other grains parents were
  easily identifiable in the wild, corns genetic
  predecessors remained a mystery.

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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.

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Can you spot the differences?
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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.

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Ear Structure

• Teosinte has 2 rows of seeds
• Corn has 8-12 rows of seeds

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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

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Why did this happen?

• Take a minute to brainstorm what could have
  caused these changes, and what could have made
  them so widespread

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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 plantmaize.

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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/artificialselectioni
  xzz2aLLKKeDP
• 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)

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Artificial Selection

• http//learn.genetics.utah.edu/content/variation/a
  rtificial/

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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.

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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.

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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!