Teacher Demo: Proper handling of seeds/plants, how to cross pollinate and how to harvest seeds and repeat the cycle using artificial selection.
1) The basic site: http://www.fastplants.org/
Our primary reason for introducing these plants to class was to give students a tangible experience with quantitative variation and heritability that would broaden their understanding of genetics beyond Mendelian inheritance and could facilitate conceptualization of natural selection in the future. Growing these plants also provided a reference for lessons in plant development, life cycles, photosynthesis, reproduction, nutrition, and experimental design. In a long term, multi-generational, experiment like this the notebooks and records that students kept became obviously and critically important. This was a simple and yet grand lesson.
An Inquiry Approach to
Wisconsin Fast Plants
Background and learning
objectives: Though development and use of Wisconsin Fast
Plants is already extensive, I found nothing about them that was designed to be
inquiry-based. Vast amounts of
information can be obtained from the web.
This includes descriptions of more than 10 easily accessible (Carolina
Biological Supply) mutant forms and a myriad of exercises. These cover different forms of inheritance,
uses of statistics, methods of measuring and understanding variation,
artificial selection, plant growth, development and flowering. These form a wealth of resources, but all are
essentially demonstration exercises.
The element of INQUIRY:
The fundamental modification we made to the design of our exercise
(close to that described in the above website as an artificial selection
experiment for plant hairiness) was to allow the students to select (given the
objective of artificial selection) whatever trait they wished: hairiness,
smoothness, height, or purple color. The
idea then changed from only observing heritability, to determining
heritability. Because height and purple
color are environmentally as well as genetically determined, this also
introduced possible questions for future B.
rapa generations. In addition to
deciding which traits would be selected, students also determined when and how
they would be measured, as well as other aspects of the experimental design
such as fertilization rates and watering schedules, etc. This offered opportunities for MANY
discussions of experimental design. I do
not believe it would have been possible to overemphasize this topic!
Materials and Equipment: Most of what is described about the necessary
growing conditions in the cited web pages is true. This should not be daunting though! You will need planting trays with
inserts. You will need grow lights. You DO NOT need extra special potting soil or
elaborate water wicking arrangements. We
did not use any plant stakes. But our
plants bent over in ways that made height difficult to measure and made it easy
for them to become tangled. Bamboo
skewers would make good cheap plant stakes.
We used pelleted fertilizer so that students could easily regulate
amounts given by counting pellets.
"Standard"
fast plant seed does not include enough variability for purple color, and ours
had only a few hairy plants. I recommend
mixing "standard" and "Purple stem, hairy" seeds for the
first parent generation. Much of the
info about the different B. rapa
traits is designed to set a teacher up for a particular exercise, without
letting on much about the mechanism of inheritance involved. What I gathered about the following basic
traits was this:
Height --- Some plants in the "standard"
mix may have tall (increased gibberellic acid) or dwarf traits. So, there could be a genetic component to
some plants' height. But, of course,
much about height will be determined environmentally.
Hairiness --- Hairs are a quantitatively genetically
determined trait only. An unknown number
of loci are involved and there is no environmental component.
Purple
Color --- Anthocyanin
expression results in purple color, which can increase in intensity as a result
of more light or reduced fertilizer. The
capability of any anthocyanin expression is a Mendelian trait for which the
homozygous recessive has none.
Ideas for Interactive
Research: Depending on growing conditions and time
allowed, several generations of B. rapa
can fit into a school year. The concept
of heritability can be addressed with one or more generations. There are also fast plant mutants that could
be explored, observed, mixed, segregated, etc.
Effects of environment, e.g. light, nutrients, crowding, can be tested
as well. If strict parental lines can be
maintained genetic questions can be followed more precisely. But this may require more plants than can fit
in the classroom!
One
idea I had that would have take several plant generations would be to test
oviposition preference for hairy or smooth lines of plants. [I was just dreaming this up when Carolina
started advertising P. rapae cultures
in combination with B. rapa
plants. They have the nerve to call P. rapae "Fast Plant
Butterflies"!!!!! In any case, they
have only raised the idea of rearing P.
rapae on B. rapa and watching
oviposition and larval development, etc.]
Pieris rapae are very easy
butterflies to rear because the larvae don't wander much at all. They stay on their host plant until they
totally consume it. And they are
beautiful! I believe they need to
oviposit with a lot of natural light, though.
If
lines of hairy and smooth plants were developed (or purple vs. green) P. rapae oviposition preference for and
larval development on the alternate plant types could be tested. This would be a great way to link the
artificial selection experiment with natural selection.
What type of Wisconsin fast plant would you have to cross pollinate with your current plant in order to express the phenotype you desire? How many generations will it take until you get your preferred results?
What type of Wisconsin fast plant would you have to cross pollinate with your current plant in order to express the phenotype you desire? How many generations will it take until you get your preferred results?
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