SUBJECT: Mitosis and Meiosis Labs
DATE: 2/95; 2/97
I'm looking for help in finding a long-term solution to a perennial problem
in our introductory labs. Our students, majors and nonmajors alike, THINK
they know all about mitosis and meiosis, because they've heard the terminology
in high school. When pressed for details, however, they're clueless. (The
worst thing is that many of our graduate TA's are clueless, too, even though
THEY think they've got it!) Even so, they uniformly despise any and all
labs that attempt to cover this subject ("we know all this," "we
did this in high school," etc.).
Here's what we've tried so far, in various combinations:
1. Prepared slides (root tip, whitefish blastula, lily life cycle), to identify
and estimate the time spent in various stages.
2. Pop-bead chromosome models (available from Carolina Biological)
3. Having students make their own squash preparations from pretreated (with
paradichlorobenzene) and unpretreated root tips, and Chlorophytum (spider
plant) buds.
I figure we've got to develop a lab that teaches them the fundamentals of
these processes without letting them know that WE know that they don't know
it yet...:) If you've had success with a mitosis/meiosis lab, I'd LOVE to
hear about it!
Thanks in advance,
Nora Ann
Nora Ann Bennett
Department of Biology
College of William and Mary
Williamsburg, VA 23187
(804) 221-2219
FAX: (804) 221-6483
EMAIL: nabenn@facstaff.wm.edu (as of 2/13)
Nora Ann Bennett asks about successful ways to teach mitosis and meiosis
in labs. While the following doesn't directly show either of those processes,
I've found students to get fairly excited (as excited as jaded intro biology
students CAN become) when beginning such labs with a human chromosome spread.
CellServ, in the Center for Advanced Training at Catholic Univ. of America,
offers a kit with cultured HeLa cells. Students can make a stained spread
and see many cells in interphase and stages of mitosis. HeLa cells are weird
because their chromosome numbers are highly variable, but students are generally
very interested in these tumor cells. This can also lead into discussion
of controls of cell division. CellServ needs several weeks advance notice
in order to produce the cells. Contact them at (202)319-5725, FAX (202)319-5721.
Address: CellServ
The Center for Advanced Training
103 McCort Ward Bldg.
Catholic Univ. Of America
Washington, D.C. 20064
The procedure for using this also appears in a Wadsworth Publishing Co.
lab manual by Perry and Morton that accompanies the biol. textbooks by Starr
and by Starr and Taggart.
Joy Perry
Univ. Of Wisconsin Center - Fox Valley
joyperry@uwcmail.uwc.edu
(414)832-2653
In reference to your problem with Mitosis and Meiosis, take a look at the
Mac program titled Mitosis and Meiosis by Intellimation at PO Box 1530,
130 Cremona Dr. Santa Barbara CA 93116-1530. I have found using their program
in class and lab has raised the learning curve for the processes in both
major and nonmajor courses. I have been pleasently surprised by the apparent
increase in understanding of Mitosis and Meiosis.
George C. Boone
Susquehanna U.
boone@einstein.susqu.edu
Nora Ann's note about Mitosis and Meiosis hit several hot buttons in me.
The first question is, I guess, what do you mean by the "fundamentals"
of these processes? Are you interested in the processes of chromosome movement,
the segregation, crossing over, etc., or the functions that are carried
out through these mechanisms.
More importantly, from my perspective, is my feeling that one should never
mention Mitosis and Meiosis in the same sentence, or the same lecture. The
coupling of the processes (because of their mechanical similarity) often
confuses students about their very different functions. Mitosis is a process
that is associated with cellular duplication, with equal distribution of
chromosomal material to succeeding generations. Its primary function is
in growth of the organism. Meiosis, on the other hand, is a rather different
process whose function is to create haploid organisms from diploid, for
the purpose of sexual reproduction.
It has always seemed to me that these processes should be presented in discussions
that are appropriate to the function of each. i.e., discuss Mitosis when
you are talking about growth, and save Meiosis for a discussion of reproduction.
Then, it is possible to discuss how Meiosis is a varient of Mitosis -that
some of the mechanisms i.e. use of a spindle, are similar, and that others,
such as the chromosome alignment, are different.
Regardless of this quibble, I find that the most dramatic way to demonstrate
the power and wonder of either process is to show some of the excellent
time-lapse videos of mitosis. Among the best images are those from Jeremy
Pickett-Heaps, but there are others. I would combine the videos with real
life observations, such as sea urchin cleavage.
Joel B. Sheffield
Biology Department
Temple University
Philadelphia, PA 19122
jbs@sgibio.chem.temple.edu or
v5415e@TEMPLEVM.bitnet
(215) 204 8854
We have used mastery quizzes with yarn models of mitosis and meiosis to
get some pretty spectacular group learning situations. At the beginning
of lab, or at the previous lab meeting, students are given a list of quiz
questions that involve the yarn models in demonstrating the answers. They
are working in groups and they are told to prepare themselves to respond
to any of the possible questions. When the group feels prepared, the individual
who will do the demonstration (take the quiz) is selected by drawing straws
and the question is drawn out of a hat (literally!).
Under these circumstances the questions can be pretty challenging. For example,
"Use a yarn model to explain and illustrate why meiosis I is sometimes
called the heterotypic division and meiosis II is sometimes called the homotypic
division. Be prepared to explain how the term'reduction division' relates
to these other terms." We didn't define any of the terms, but gave
students access to a dictionary. Another question I liked was "Using
a yarn model for an organism with 2N = 4, create two gametes with distinctly
different chromosomes. Work the model through one generation, producing
gametes unequal in numbers of grand-paternal and grand-maternal chromosomes."
Groups really sought out instructor help, which was freely given but only
through aggressive questioning (What does this represent, What happens next?)
and once they had worked out a solution, group members took turns quizzing
each other on it, and often got into questioning each other rather aggressively
also. It worked. We've done it with and without actually giving a grade
for the final performance. The approach works just as well with questions
related to microscopy preparations.
Robert B. Ketcham rketcham@strauss.udel.edu
Department of Biology (302) 831-2377
University of Delaware
Newark, DE 19716-2590
I have made a number of chromosomes from poster board that I have colored
with different colors of magic markers to indicate dominate and recessive
alleles. I give each set of students a diploid set and then tell them to
prepare to undergo mitosis. It usually takes them a minute to realize that
they need to replicate them first. I then distribute another set to represent
the replicated chromosome (they are given tape to hold the sister chromatids
togather, but velcro would be easier). I then have them sort the chromosomes
at each stage and we move through the class to make sure they have the chromosomes
lined up properly. At the completion of mitosis, we find out how many cells
we end up with and what is their gentic constitution compared to the parent
cells This seems to help students visualize the sorting process.
For meiosis we start over again with replication again (this time they catch
on right away). We then tell them to arrange the chromosomes as they might
appear at prophase I, metaphase I, anaphase I, etc. At this point we let
them make mistakes in segregation (that is we do not correct their mistakes)
so that we can illustrate the proper segregation of chromosomes. We then
have them complete meiosis I and meiosis II and we then take a poll of the
class to determine the genetic constitution of each of the daughter cells.
If we have a large enough class, this allows us to nicely illustrate recombination
and distribution of alleles. This is especially important for us because
the next week we deal with genetics.
--
James M. Bader
Asst. Director, Center for Biological Education
Case Western Reserve University
jxb14@po.cwru.edu
I use post-it notes in my non-major's class to help demonstate WHY chromosomes
pair during meiosis. Students label a set of post-it notes to represent
a pair of alleles. Initially I have them scatter them randomly on a table
top (up-side down). Working in pairs, each student picks up half of the
notes. Even with just three sets of genes it is rare that a student gets
one copy of each gene. I then have them stick the alleles together and repeat
the selection. This time each student gets one note from each of the pairs.
Of course, they both must get one of each allele using the paired notes.
I have also had students attempt to model the process of meiosis using post-it
notes, but frankly I do not think that the steps of the meiosis are as important
as the logic of the process.
Richard Weisenberg
Dept. of Biology
Temple University
I'm glad you brought up the subject of teaching mitosis and meiosis. we
haven't solved the problem, but I second the idea of using time lapse films.
We have several antique film loops of both processes and they really do
help to get the idea across. I also put out sets of photographs of the different
stages of meiosis which are labelled on the back. I tell the students to
examine them and then to shuffle the photos and try to get them back in
the correct order without looking at the labels. We also do a root tip squash
and pipe cleaner chromosomes. But my favorite is the "Dance of the
Chromosomes". I divide the students up into sets of eight and label
them either A, a, B, or b. Then I tell them to go outside and pretend to
be chromosomes going through meiosis. I let them figure out what to do with
the minimum of direction and then have each group perform for me. Most of
them find this silly but fun, and even the ones who feel it's rather an
affront to their dignity have grudgingly admitted that it did help them
to visualize the process. I certainly enjoy it. Good luck and please pass
on any ideas you find work.
Susan Schenk
Claremont Colleges
Claremon, Ca
sschenk@jsd.claremont.edu
We do the 'dance of the chromosomes as well here at Bates. Yes, its silly
but they really do enjoy it. We prep them for this dance by having them
watch a video of a humerous dance/skit filmed by a senior rhetoric student
a few years back......she needed a science credit to graduate and we had
her produce the mitosis/meiosis skit as part of her effort. After all that
work...she REALLY does understand the two processes.
Joe P
--
Joseph G. Pelliccia PP-SEL-IA * "A beginning is a delicate time"
Chairman, Department of Biology * -Princess Irulan
Bates College, Lewiston, ME 04240 * DUNE
I've been following the Mitosis and Meiosis thread and my understanding
of Nora's problem is not so much How to teach this material but rather,
How to keep students who have an inflated sense of their understanding open
to further exploration?
I have had good success with using cancer biology as a hook to get them
into cell cycle/cell division material without ever saying the m-words.
Sometimes I come at it from forensic toxicology. What would you expect to
find in tissue killed by colchicine? I like to hook them with nice-to-know
mind-candy and then I build in the need-to-know biology. (Of course I'm
clear with them about which is which.)
In the lab, I think it is hard to beat some type of investigative exercise
in these situations.
How about giving someone a handful of beans or a spider plant (or prepared
slides), a microscope etc. and expect them to ask a question for which they
can find an answer with the tools provided. Yarn models, pop beads, video,
modelling clay, and chromosome dancing etc. may all be used for background
or to help make predictions. The theory goes that if students can be sold
on asking their own questions and then doing their own science they will
admit/discover their misconceptions and work to straighten themselves out.
This has been my experience with a large Year 2 genetics class.
We have done investigative style labs with the Vicia root tips/colchicine
system. Students investigated questions relating to the proportion of cells
in various stages, chromosome condensation, mitotic index variation in different
root tip sections as well as effects and kinetics of colchicine treatment.
There are also estimates of chromosome number and karyotypes etc. to be
done.
I would like to expand our repetoire in this area. I'd appreciate further
information on the spider plant bud exercise as well as leads on other cytogenetic
systems that would lend themselves to student questioning. (Preferably not
involving scraping marrow out of the broken bones of furry animals).
Tom Haffie Phone: 519-679-2111 (6502)
Department of Plant Sciences FAX: 661-3935
University of Western Ontario e-mail: thaffie@julian.uwo.ca
London, ON, Canada
N6A 5B7
Tom,
For Chlorophytum, 2N = 28.
Nora Ann
Nora Ann Bennett
Department of Bioloyg
College of William and Mary
Williamsburg, VA 23187
(804) 221-2219
email: nabenn@facstaff.wm.edu
I agree with Joel Sheffield that the key to making mitosis/meiosis labs
work is knowing what it is you are really trying to stress. I disagree with
the idea that mitosis and meiosis shouldn't be mentioned together, precisely
because they are so easily confused- I think the best way to teach students
to discriminate between two similar things is to put them side by side and
carefully point out the differences.
In contrast to Nora Ann we've had success with the Carolina popit beads
(we used to use pipe cleaners to simulate chromosomes but the beads are
better for showing crossing over). I have the students start by making a
model of a G1 phase nucleus with single chromosomes as a reference. They
then work together to make models of the various phases of mitosis ending
with 2 daughter nuclei. They should then see that the daughter nuclei are
identical to the reference nucleus. They then repeat the process with meiosis
and find that this time they end up with 4 haploid nuclei that are all different
from the reference and (thanks to crossing over) different from each other.
The time and effort they invest in making all the models lined up together
on the bench top and the graphic differences in outcome seem pretty effective
in helping them remember which process is which and what each process is
good for.
I haven't encountered too much resistance from the students. They're often
so confused after the lecture hall presentation on M&M that they are
happy to have a hands on opportunity to straighten it out. TAs are another
matter. In the prelab meeting I tell them that even though they may have
mastered this as freshmen, that was years ago and they probably haven't
used it much since then. I urge them to review before they get in front
of their classes rather than let themselves look stupid by getting confused
at the last moment. Since I can tell them that this has happened in the
past several times and that the TAs involved really did feel pretty embarrassed,
they generally heed the warning.
John Dickerman
Biology Lab Coordinator
Northern Illinois University
T80JWD1@WPO.NIU.EDU
(815) 753-3101
I'm looking to have students design their own study of cell division (thinking
of next Fall). How much time do you allocate? I'm thinking of 2 to 3 weeks
(1 3hr lab per week), to introduce the technique of staining and squashing
a root tip, time for students to confront the decisions necessary for testing
the effects of a chemical, and a full lab to execute.
Do you send your students out to do some research into methods - chemicals
to use, concentrations, length of exposure, etc.? Are all your studies looking
at the effects of a chemical?
Do you let them develop their own methods of quantification? Do you always
use squashes or are you doing sectioning? Squashes are so easy and they
are fine for catching cells in interesting poses, but students get befuddled
when asked to do counts/area or percentages - the sampling question of what
is a suitable area is a stumper. The crisp geometry of thin section makes
this easier but too much is lost in the transition from squash to commercially
prepared slides - the latter are no longer the students' project.
Related to the quantification, one of the appeals of doing this experimentally
is the opportunity to address bias in sampling. Students can do a 'blind'
study, which to me is the solution for the sampling problem. But I've found
students don't discover this on their own. What do you do?
We've been using onion sets, which are great. We can give a student a set
in a bit of vermiculite in a cheap plastic drinking cup and tell them to
moisten vermiculite thoroughly 2-3 days before lab and Bingo! students have
prepared their own material. [Actually we have yet to do this with the students.
We did do it with the instructors and its so easy it would work with students
(next year). This year I encouraged instructors to have their students use
this material in experiments but none did - they used it for things like
quizzing students on microscopy.] Do you have students sprout their own
beans?
As I understand it, seedling roots of many species will work. Grocery store
sprouts don't, unfortunately - they aren't growing any more. I'd be interested
in hearing about materials that others use.
RKetcham/UDelaware
At the risk of this thread turning into a knot, I'll respond to Bob
Ketcham's posting about M and M labs;
>
We've had pretty good luck with introducing the I-lab as creative tool-using.
Our standard format is to make a big deal of the central role of questioning
in research and the nearly complete absence of questioning in science education.
We are very direct with students that I-labs require the use of unfamiliar
tools as well as familiar tools in unfamiliar ways. We set them the task
of asking their own questions and then assure them that much help is available.
We meet for 2 hr early in the week and then again for 3 hr later in the
week.
In lab #1, we open with some community building among students and instructors
and then set the general biological stage - the conceptual tools - videos,
brainstorming, concept maps etc. Then, just as people get restless, we break
out the technical tools and roll up sleeves for the rest of the (first)lab.
Lab #2 is devoted entirely to a "dry run" of the techniques for
practice - similar to a standard "cook book" lab. This exercise
may also provide data or material to be used in future labs. During down
times in the protocol, we mingle and discuss how these techniques might
be applied to their own questions.
Before lab #3, many students worry and fret about their research question
but at least they arrive in an attentive frame of mind. We then spend some
time on general experimental design with some specific (obvious) examples
that pertain to the system being studied in the lab. In this "design
lab", I have a 36 students and 3 - 5 well briefed instructors. It is
an intensive, hand to hand, one on one, small group, teaching environment
that leaves everyone exhausted. It's great! In reality, there are only about
6 or 8 appropriate questions and the 36 individual students coalesce into
subgroups based on common interest.
Lab #4 and #5 is devoted to confirmation of designs, experimentation and,
perhaps, for extensions or repeats of the original designs. Students collaborate
for the technical work if they like. Groups of 1 to about 5 depending on
the design and personalities.
Lab#6 is time for making sense of the data and marshalling the persuasion
tools to be used in Lab #7 to convey the science to instructors and peers
in a Symposium. We use such instruments as oral presentations, poster sessions,
and personal interviews as well as some some of writing.
This probably sounds like a luxuriant amount of time for one exercise but
we are also working specifically on scientific writing and a GCK exercise
is playing out in the background. Students then move from my genetics area
into a 4 week session in ecology and then another session in cell biology.
>Do you send your students out to do some research into methods -
>chemicals to use, concentrations, length of exposure, etc.? Are all
your
>studies looking at the effects of a chemical?
We do our best to assume only background covered in prerequisite Year 1
biology courses. Specialized information or data that might be expected
to
arise from a preliminary experiment is often provided or referenced as
appropriate.
Chemicals are just one of many variables that we use to broaden the range
of good questions that can be asked.
>
>Do you let them develop their own methods of quantification?
We would present established methods as a "tool".
Do you
>always use squashes or are you doing sectioning?
Squashes only. We satisfy ourselves with very crude scale (1 mm +) sections
for sampling.
I am mostly concerned with the thinking that goes on in the lab. If a student
can ask a good question and find the answer by analysing prepared slides
then I'm happy. They have done the technical practice session - I can let
go of the rest.
>
I lead them into discovering such things on their own with a couple of well
aimed criticisms of their designs. I point out how they will be vulnerable
when it comes time to present the data to peers.
>Do you have students sprout their own beans?
We didn't, but we will. I'm anticipating the look on their faces as their
initial confusion clears as they figure out that they can get cycling cells
by germinating the seeds.
Sets sound great. How many chromosomes? Big ones?
>As I understand it, seedling roots of many species will work.
We are having some difficulty finding shoots with few, fat chromosomes.
Vicia faba is wonderful, Corn is OK, Some types of peas are OK. Commercial
crop species tend to be polyploid.
Tom Haffie Phone: 519-679-2111 (6502)
Department of Plant Sciences FAX: 661-3935
University of Western Ontario e-mail: thaffie@julian.uwo.ca
London, ON, Canada
N6A 5B7
Tom, thanks for the detailed reply. I really like what you are doing and
would love to dig even deeper into specifics but perhaps that should be
done as a private chat at a future time.
I would like to pick up on one thing you say and turn it into a general
discussion if others can offer insights. It has to do with having students
work in groups. As I read Tom's description, his students are talking, thinking,
questioning, and practicing techniques for the first 3 labs, and this involves
small group interactions, probably of shifitng compositions. When they lock
in on their own investigations, in labs 4 and 5, they work collaboratively
at their own discretion ("Students collaborate for the technical work
if they like. Groups of 1 to about 5 depending on the design and personalities.")
I would like to have this happening in my labs, but I'm not there yet. We've
used groups for several years, but have been in a more structured mode.
We assign students to a group (5 per), have each group write a 'group contract'
in which people define the level of commitment they are willing to make
to the group effort of designing and conducting an investigation. This is
not bad, and I will probably continue to start the course this way (freshman,
by the way), but I would like to move on to a more voluntary arrangement
of groups. What I'm guessing has to happen is that the whole lab section
needs to be functioning as a group at the beginning - working in one area,
exploring what they do and do not know already, exploring possibilities,
and drafting potential experiments - the give and take, trial and error
preludes to making decisions. Then they can break out into voluntary groups
to do different things, but they will still be able to talk and consult
across groups, and will be able to communicate their results to an informed
audience. As I say, I'm just trying to work these things out for my situation.
Tom Haffie's comments gave me a boost of confidence (thanks again, Tom).
I wonder if others agree or disagree with the reasoning.
Tom, you did ask a specific question about the number of chromosomes in
the onion. As my daughter would say, DUHHHHH! I think its in the twenties
(26?) - that would fit with what I saw, probably countable but not easily.
Maybe someone else has the number at hand?
rketcham, Univ. Delaware
According to the Chromosome Atlas of Flowering Plants, most
species of onion (Allium) have 2N=16, but the number varies
from 14 to 48. I knew this book would come in handy!!
--
James M. Bader
Asst. Director, Center for Biological Education
Case Western Reserve University
jxb14@po.cwru.edu
Several years ago, we decided to have our non-majors make their own slides
to observe mitotic figures rather than looking at prepared slides. We found
that onion roots worked pretty well, but that narcissus roots worked even
better. The cells in narcissus roots are larger with correspondingly larger
chromosomes than onions. Almost everyone in class got a nice prep with visible
figures.
Narcissus bulbs should be prepared 48-72 hours before lab. To stimulate
root growth, lightly scrape off (with a scalpel) the roughly circular callous
found within the circle of old roots. Then place the bulb in water. In a
warm room, roots should begin to grow after about 24-36 hrs and be usable
in 48. After the roots have reached about 4 cm or so, mitotic figures are
difficult to locate The only problem with using narcissus roots is that
the bulbs are not available year round. However, they will keep in the refrigerator,
so you can purchase them ahead of time.
Not only do narcissus roots have larger chromosomes than onions, but in
another week or so, you have beautiful flowers!
Doreen Schroeder
Department of Biology
Mail # 4327, University of St. Thomas
2115 Summit Ave.
St. Paul MN 55105
I've really enjoyed the discussion on M & M labs, particularly the investigative
labs done by Tom Haffie and planned by Bob Ketcham. Their discussion has
inspired me to bring mitosis back into the laboratory. We used to do one
lab on cell division and the cell cycle using onion bulblets purchased at
garden stores or home improvement stores (just wrapped them in moist paper
towels for 1-2 days). Students made their own squashes, and calculated mitotic
indeces and the duration of each phase (based on a 16-hour cell cycle for
onion). However, it was at this time that one of the lecturers in our team-taught
course kept on trying to squeeze mitosis out of the lecture entirely, suggesting
that it be covered solely in a demonstrative lab complete with an intro
lecture by me. Being that I was in a contrary mood at the time, I argued
that a non-investigative lab was what I was trying to get away from, and
that mitosis should be taught in lecture, using some of the techniques (pop-it
beads, yarn, dances, shuffled pictures) that have been discussed here. This
would provide a chance to do some group work and active learning in lecture
-- a great break from the "normal" lecture routine. I ended up
dropping mitosis entirely from the lab last year -- to create more space
for 2-3 week investigative labs. Now, Tom's and Bob's ideas will push me
to try and bring back mitosis and cell cycle next year as a several week
investigation. Thank you!
(Incidentally, we teach mitosis & meiosis separately. Meiosis is covered
in our "organismal" fall course when Mendelian genetics is taught,
and mitosis is taught in our "cell/molecular" spring course when
we discuss the cell cycle.)
It seems we constantly battle with trying to blend (at least!) 2 goals of
the teaching laboratory: allowing students to more fully comprehend concepts
presented in lecture by hands-on experience with those concepts after lecture;
and allowing students to experience and learn the critical thinking skills
used in science by designing, performing, and analyzing their own experiments,
often with no regard for what's being covered that week in lecture. I find
it very hard to have a few "investigative" labs in a row, and
then go back to a "concept-reinforcing" lab -- the students often
object. On the other hand, if I have a few concept-reinforcing labs in the
beginning, and then switch to investigative labs, students argue that they
need and rely on the laboratory to help them with the lecture material.
I tend to lean towards (if not exclusively) the investigative lab, but then
feel guilty that I'm not doing all I can to help students with as many concepts
as possible from lecture. Do many people try a mix of the 2 types of labs?
And if so, how do students respond? If you use all investigative labs, do
students complain that "lab has nothing to do with lecture" much
of the time?
Mike O'Donnell
Dept. of Biology
Trinity College
Hartford, CT 06106-3100
michael.odonnell@mail.trincoll.edu
Mike O'Donnell laments that his students complain that the investigative
labs have nothing to do with the lecture. Maybe the problem is with the
lecture!
Tom Haffie
thaffie@julian.uwo.ca
Thank you all for the wonderful discussion of mitosis and meiosis!
I heartily agree that mitosis and meiosis are too often lumped together,
leading to massive confusion. In fact, I've argued that we should do as
Mike O'Donnell suggested (our cell/molecular course is in the fall, and
the genetics/ecology/evolution in the spring):
> (Incidentally, we teach mitosis & meiosis separately. Meiosis is
covered
> in our "organismal" fall course when Mendelian genetics is
taught, and
> mitosis is taught in our "cell/molecular" spring course when
we discuss the
> cell cycle.)
Currently we do a semester-long inter- and intraspecific competition experiment
with Drosophila population cages. One cage has two species of Drosophila,
and the other has two morphs of the same species (red vs. white-eyed melanogaster).
The students sample the cages weekly, then graph and analyze the data at
the end of the semester. The weakness of this lab is that each lab section
has one set of cages, and a different group of students samples each week.
They don't really see any continuity, and they don't "get it"
until the end of the semester when we pool the data for the semester. With
over 400 students, though, we can't afford a cage for each group of 4-
6 students.
Tom asked about the spider plant bud exercise. This procedure was written
by Stan Hoegerman, our cytogeneticist. Collecting the buds is the tedious
part. We've got about a dozen plants in the greenhouse, and we collect the
buds sporadically. We pick them with tweezers, and drop them into a fixative
of 3 parts ethanol to 1 part glacial acetic acid. The fixative should be
changed daily until it's clear (the chlorophyll, etc. will leach out). Once
you've got clear fixative, you can store the buds indefinitely (from one
year to the next).
In lab the students select a flower bud, place it on a microscope slide
in a drop of 45% acetic acid, and dissect out the anthers (with freshmen
we've got to be very careful to show them what they're looking for, since
they've never had a botany class...). Once they've isolated the anthers,
blot the acetic acid, and add a drop of aceto-orcein stain. Macerate the
tissue with dissecting needles until you've got a fine pulp. Add a cover
slip. Most of the cells will be in the same phase of meiosis, but different
students will have different phases.
Our goal for this lab is much the same as when we have the students do their
own root tip squashes: that they see where this process actually occurs,
and that they learn some cytogenetics techniques.
I've enjoyed this discussion, and I thank you all for your generous comments.
Nora Ann
Nora Ann Bennett
Department of Biology
College of William and Mary
Williamsburg, VA 23187
(8040 221-2219
email: nabenn@facstaff.wm.edu
This should have been sent long ago when the topic on the table
was cell division, but for what it's worth, here it is.
I didn't see any mention of the very useful technique developed
by Joe Nickolas, Northland Community College, Holbrook, AZ, for
staining root tip squashes from Zebrina spp.(Zebra plant, Wandering
Jew, etc.). We have had great luck using this technique and we
especially like the fact that the students start with living
root tips and have a stained squash in about ten minutes.
The first-time success rate is high, but the short preparation time means
that "do-overs" don't cause unreasonable delays in the work if
students don't get good preps the first time. The preps
are pretty durable, too. I tried sealing the cover glasses
on several student slides and observing them after storage.
There were still decent, visible mitotic figures after several
weeks.
Now, the question. Was this technique, which was originally
presented at an ABLE mtg., ever included in an ABLE volume?
If it wasn't, maybe Joe could be imposed upon to put it on
this bulletin board. I think that many people would like it as a
replacement for some of the messy, smelly techniques that
employ pretty nasty fixatives or preservatives, or both.
Leland Johnson
johnson@inst.augie.edu