- SUBJECT: Tips on Drosophila labs
- DATE: 3/97
-
- Hi, I'm looking for the practical answer to a question. I have an
- undergraduate working with me who is interested in developing a genetics
- lab using drosophila. The lab would be used in a non-majors lab that
meets
- for 2 hours a week. What are the tricks? What are the pitfalls? What
- traits are easiest to follow? -- cmw
-
- Charlene M. Waggoner, Ph.D. "Great art is eternal;
- Department of Biological Sciences great science tends to be
- Bowling Green, State University replaced by greater science."
- Bowling Green, OH 43403
- -- John A. Moore
- cwaggon@bgnet.bgsu.edu
-
-
- Hi Charlene! The key to making this work is to have at least 2 lab
periods
- devoted to it. We have found that the only way to religiously get good
- outcomes is for me to actually set the crosses and give them to the
- students as the F1s are emerging. The students then count the F1s and
set
- the F2s on their own. Granted, I'm dealing with 32 sections at a time
- taught by very novice TAs so on smaller scale the students may be able
to
- collect their own virgins and set crosses but it just doesn't work
for us.
- I've also learned to leave 3 weeks between setting crosses and counting
- instead of two. If the lab rooms happen to be chilly, two weeks can
give
- really skewed sex ratios since females emerge first. Three weeks is
long
- enough to avoid that problem and short enough not to worry about an
- additional generation happening. We like to use white eyed, vestigial
wing
- in reciprocal crosses with the wild type; however, this strain is not
very
- hardy and we have had considerable problems maintaining enough crosses.
- Anybody else having trouble with this mutant? For non-majors I'm not
sure
- I would attempt a dihybrid cross. Apterous wing mutants are really
easy to
- score for a mono-hybrid cross.
-
- Chris
- V. Christine Minor
- Biology Laboratory Coordinator
- Iowa State University
- 154 Bessey Hall
- Ames, IA 50011
- 515-294-8596 vcmahaff@iastate.edu
- http://www.biology.iastate.edu/
- In our intro labs (2 hours) we do the fruit fly lab as described by
- Chris, except we devote 3 lab periods and do several additional
- crosses - the third lab period is to allow groups to present the
- findings of their own cross.
-
- WRT the problem below, yes we also have low yields. We think the
- cause is the low rel. humidity of the labs in the winter, and we are
- thinking of doing this lab in the fall.
-
- >>additional generation happening. We like to use white eyed,
- >>vestigial wing in reciprocal crosses with the wild type; however,
- >>this strain is not very hardy and we have had considerable
problems
- >>maintaining enough crosses.
-
- Graham R. Kent
- Dept. of Biological Sciences
- Smith College
-
-
- Graham-
-
- Building humidity is not your only problem. We do the experiment spring
- and fall and I've tried nearly every month available in those semesters.
- Close monitoring of the cultures and nearly daily adjustment with more
- water or more food is the only way around the food dryness/wetness
problem.
- I have gone so far as to outcross my mutant strain and bring it back
again
- in hopes of restoring a little vigor but I get the same wimpy flies
every
- time. The interesting thing is that each trait alone is quite vigorous
and
- does as well as wild type but when you get the two mutant traits in
one fly
- its almost impossible to keep them alive 72 hours post emergence. Around
- here "fly week" is designated as the week no one sees me
as I try to get
- enough for crosses. This year my 2.5 year old said to her pre-school
- teacher "Mommy not home. She makin flies." No wonder they
look at me
- oddly!
-
- Chris
- V. Christine Minor
- Biology Laboratory Coordinator
- Iowa State University
- 154 Bessey Hall
- Ames, IA 50011
- 515-294-8596 vcmahaff@iastate.edu ..
- http://www.biology.iastate.edu/
-
-
-
- We've been doing a fruit fly lab for years at Bates College. Several
things
- we've found:
- Most of us use dehydrated food (ex...Carolina 4-24). This food is very
- sensitive to dehydration unless you put in a large number of adults
who will
- quickly begin to lay eggs (as the hatching larvae will keep the food
moist).
- Dry food is also much more prone to bacterial/fungal contamination.
- Few of the classical mutations used in undergraduate Drosophila work
will
- give the standard 3:1 Mendelian ratio in a monohybrid cross as most
mutant
- strains are less viable(at least when competing in a crowded food vial
against
- their wild type counterparts). They may also take longer to develop
so unless
- the whole F2 cohort is captured, the data will skew towards the wild
type.
- Yellow body (sex linked) is a good exception to this, but in our hands,
- vestigial wing, white eyes, ebony body, and black body all show less
than
- Mendelian ratios.
- Rather than lament this deviation from ideal behavior, we try and get
the
- students to come up with explanations for why this might be.
-
- Joe Pelliccia
- Dept. of Biology
- Bates College
- Lewsiton, ME 04240
- jpellicc@abacus.bates.edu
-
-
- The EASIEST way to go is to buy F1's from WARDS. Then the students
- can do one generation to get results. Other advantages are that you
- don't need to collect virgins, and it really doesn't matter if they
- mis-sex some of the flies. Both are important if you start with
- two different parental strains.
- -Bob Moss
- Wofford College
-
-
-
-
-
- We've had good success using Drosophila in the Genetics unit of our
=
- introductory course for Biology majors.
-
- Traits that are easy to work with include:
- white eyes - sex-linked, recessive
- sepia eyes - recessive=20
- vestigal wings - recessive
-
- Tricks:
- To immobilize the flies while they are examined, we first knock them
=
- out with carbon dioxide. (We keep a tank of compressed CO2 in the lab.)
=
- The flies are then kept quiet by placing them on cold petri dishes.
=
- The petri dishes are placed on top of a bowl of ice, so that they stay
=
- cool. As long as there is ice in the bowl, the petri dish says cool,
=
- and the flies stay quiet. The Students exam the flies under a =
- dissecting scope and move the flies around with fine watchmaker forceps,
=
- picking them up gently by their wings.
-
- Pitfalls / things to consider:
- Initial crosses require virgin female flies. This is b/c Drosophila
=
- females can store sperm from one insemination and fertilize her all
her =
- eggs with it. To ensure a pure cross b/n different strains unmated
=
- females must be used. The collection of virgin females requires some
=
- time and diligience, if you're going to collect them yourself. Perhaps
=
- virgin female flies can be purchased. To collect virgin female flies,
=
- stock vials of flies are emptied in the morning of all adult flies.
In =
- the afternoon, the vials are checked for any adults that may have =
- emerged from their pupa during the day. The males and females are =
- separated, and the females are kept in a separate vial. Since the flies
=
- do not sexually mature til several hours (8 - 10 hrs.) after emergence,
=
- these females can be considered virgin. The absence of larva in the
=
- vials after several days will confirm the virginity of the females
in =
- the vials. This is probably the most critical part of Drosophila =
- experiments. Results will obviously be throw off if the females used
=
- are not virgins. We train our students to collect the virgin flies
=
- themselves. In a course with a greater number of students, this may
not =
- be feasible. It may be possible to purchase virgin females from a =
- supplier.
-
- Another thing to consider is the length of the experiment. Since most
=
- of the popular strains are recessive, two generations are required
to =
- see recessive phenotypes in the offspring. The generation time is two
=
- weeks.
- So, our experiment schedule goes like this:
- week 1: Set up the crosses
- week 2: Remove the parent generation
- week 3: Exam the F1 generation, set up crosses of F1 x F1
- week 4: Remove the F1 generation
- week 5: Exam the F2 generation
-
- Since the work required in weeks 2 and 4 is minimal, we use these lab
=
- periods to introduce the chi-square analysis the students use to analyze
=
- their results.
-
- Virgin females are not required for the F1 x F1 cross, b/c the females
=
- will be reunited with males of the same generation in new vials.
-
- Different crosses can be set up. We have our students do the following
=
- crosses:
- wild type x vestigal winged
- wild type x sepia eyed
- wild type females x white eyed males
- wild type males x white eyed females
- vestigal winged females x sepia eyed males
- sepia eyed females x vestigal winged males
-
- Any number of different crosses can be set up. You could specify the
=
- crosses or let the students come up with their own crosses. We have
our =
- students analyze the results of the vials they set up, as well as the
=
- pooled results of the entire class.
-
- Ward's does sell F1 flies that can then be mated with each other. This
=
- would significantly shorten the length of the experiment. Give Ward's
=
- sufficient notice to set up the crosses and collect the F1 generation.
-
- Drosophila are easy to maintain; simply move stock collections to fresh
=
- vial every two weeks. Several concepts can be highlighted in these
=
- experiments including posing an hypothesis, statistical analysis, =
- advantages of pooled data, etc..
-
- That's all I can think of off the top of my head. If you have any =
- further questions, don't hesitate to inquire.
-
- Ron van der Heiden
- Redeemer College
- Ancaster, ON
-
- rvdheid@redeemer.on.ca
-
-
-
- Dear Biolabbers:
-
- We have been doing fruit fly crosses here at Elon in our population
- biology lab. We have eliminated most wing mutants because they don't
do
- well as others have indicated. We have had very good ratios with white,
- sepia, and ebony. The sepia and ebony phenotypes are hard to confirm
in
- very young flies so I have my students transfer offspring to a fresh
vial
- and count them when they are at least 24 hours old.
-
- Another problem students have is in the making of culture medium. They
- usually put in too much yeast. Three or four grains are plenty, more
can
- kill the flies. Carolina Biological told me that the flies carry some
- yeast on their feet from culture to culture so it's usually ok if you
- forget to add it.
-
- I take the vials home the night before I need virgins in the lab and
dump
- the adults out before I come to school. That way, by lab time (1:30)
- there are usually plenty of flies for them to sex (if I timed it right).
- It really helps if you have many vials to collect from (2 or 3 per
- student group). The extra work is worth it as some will have more
- virgins than others. I have groups of 2 sex one phenotype and then
swap
- males with another group to do reciprocal crosses. I insist all sexed
- flies be checked by the instructor or the TA before they are placed
in
- vials for mating. We have had few mistakes this way, but the mistakes
make for
- interesting class discussions.
-
- Kathy Gallucci
- Elon College
- Elon College,NC
-
-
- Many, many years ago as a grad student in charge of fruit fly crosses,
I
- discovered in the literature that eclosion (I think that means emergence
- from the pupal stage) is on a biological clock with most emerging around
- sunrise. I was able to gather virgins more conveniently by putting
the
- cultures in a light-tight room with the lights on a timer set for dawn
at
- 12 noon. Clearing of the bottles could be done at a convenient time
in the