Teosinte Case Study GPS: S7L5. Students will examine the evolution of living organisms through...

Teosinte Case StudyTeosinte Case Study

GPS: GPS: S7L5. Students will examine the S7L5. Students will examine the evolution of living organisms through inherited evolution of living organisms through inherited

characteristics that promote survival of characteristics that promote survival of organisms and the survival of successive organisms and the survival of successive

generations of their offspring.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 by-product as an ingredient!

King Corn: http://www.youtube.com/watch?v=nvMxIEgbsIo&wide=1

Start at min. 3:03 – 4:30

Just so you know…

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/variation/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!