Author: ____Rachel Meyer________________ Date: ____2.4.2012_______ Act. #__3_____
This activity is meant to give students exposure to what the main changes in plants from wild to domesticated were. There are only about eight main ways we change plants to become better as foods. This is providing the foundational content for the rest of the course.
Estimated Time of Activity: 90 minutes
Goals: Process Skills, Content Knowledge, Attitudes:
...learn the 10 domestication syndromes
...learn what "correlation" is, that it is a trend, not necessarily a cause
...learn about the genes that control fruit size: particularly , FW2.2
Continue working with the Meyer, DuVal, and Jensen paper. Make sure students have the heat map.
Share a few copies of Tanksley et al FW2.2 paper toward the end of the activity.
Pre-Activity: (10 minutes)
Do a brainstorm of what we think wild versions of the Rose family looked like:
The rose family (Rosaceae) includes crops like apple, quince, cherry, peach, apricot, raspberry, blackberry, and pear.
The common changes, in this case, larger fruit size, sweeter, and different flavors, are a domestication syndrome. Actually, they are two domestication syndromes: a change in fruit size, and a change in "metabolites" or the chemistry of the plant tissue, in this case the flavorful compounds in the fruit.
- Divide students into groups, and have them find a crop plant they are familiar with for each domestication syndrome (20 min). These are within the matrix used last lesson. Use the "category rationale" file for broader definitions of the syndrome.
- Informally discuss (15 min)everybodys examples, make sure everybody understands all the syndromes. Take time on this. See the teacher's notes for guidance on the difficult categories. This content is crucial
- OPTIONAL EXTENTION ACTIVITY (20 min) : If you have time it is nice to think about domestication syndromes in animals. Here is a video students could watch on dog and sheep domestication syndromes. They can discuss and DEFINE the syndromes. Then show them this video which is on the domesticated foxes, and see if they can confirm their definitions.
- Hand out the copies of the FW2.2 paper (15 min). Have students read the paper, preferably at least through the first half. Go through diagrams and figures.
- Pass out some different-sized tomatoes to groups of students (15 min): cherry tomato, medium size, and large tomatoes. Give students knives (yes...butter knives is fine) and have them dissect the fruits. Do they see the changes reported in the FW2.2 paper? What else do they observe (see instructor notes).
- Wrap up with discussion about domestication syndromes of tomatoes.
Domestication syndromes are as follows: 1)change in fruit size, 2)change in above-ground vegetative features (like leaf size, or woodiness), 3) change in below-ground structures ( like big root size), 4) change in breeding system, 5) change in ploidy (like for bigger cells, like strawberry or wheat), 6) change in metabolites/flavor, 7) change in timing (like perennial to annual), 8) change in seed retention (non-shattering like rice)..
No formal assessment, just participation.
While some domestication syndromes are straightforward, others are really difficult. For example, one example of the change to the breedign system isparthenocarpy, where a plant can produce a fruit without being fertilized by pollen, is difficult for students to grasp. If you want, eliminate these difficult categories. But it is not that hard to explain them with examples with banana, and seedless varieties of watermelon. Hormones and many genes involved in signalling pathways signal a plant to still produce a fruit even if it will have no seeds. See wikipedia http://en.wikipedia.org/wiki/Parthenocarpy for more information.
Other changes to the breeding system are switches from outcrossing (needing pollen from a different plant) to self-fertile plants. Potato is a good example of a plant whose wild ancestor was not self-fertile, but cultivated forms are self-fertile. Maybe spend some time discussing the advantages of this (i.e. you don't have to pollinate the flowers yourself, like corn, or you don't have to worry so much what the seeds will be like (if both egg and sperm are from the same parent, the offspring are more likely to resemble the parent, or for it to 'breed true').
On FW2.2: when students dissect the tomatoes, here are some questions you can ask them that will help them deepen their explorations:
- Which tomatoes have skin that breaks the most easily? Does this have implications for transport?
- Peel a little piece of the outer cuticle, i.e. the skin off each tomato. Are they the same?
- Which tomatoes have the most chambers?
- Which tomatoes have the thickes cell walls?
- Do they smell the same? Taste the same (maybe you can't sample them depending on class rules)?
- Do they have similar seeds? Similar numbers of seeds? What about the mucilage around the seeds?
- Are the colors of the different tissues in the fruit the same?