[Drosophila] Mutation not as described

Gae Kovalick kovalick_g at utpb.edu
Thu Jul 21 13:08:06 EST 2005

I'm studying changes in Drosophila midgut morphology immediately following
eclosion.  I've looked at wild-type flies, and now I'm examining the process
in various mutant strains.  I have a very interesting mutant that I am
trying to work with, but it doesn't seem to be behaving as the published
literature suggests it should.  I was hoping that someone could give me some
insight into what is going on.

There is one published paper on this particular mutation.  The mutation is
described as being both viable and fertile.  The mutation occurs in a gene
on the X chromosome, and a stock bearing this mutation is available from the
Bloomington Stock Center.  This is the only mutant allele of the gene.

I ordered the stock from the Stock Center.  The mutant chromosome also has
recessive alleles for y and w.  The stock also carries the balancer
chromosome FM6 that has recessive w and ct alleles.

I established a stock from the flies I received from Bloomington.  When I
examined these flies, I found females that were homozygous for the mutant
chromosome and males that were hemizygous for this chromosome.  These flies
were yellow and white, but lacked the mutant phenotype.  I did find a few
males that had the mutant phenotype.  I tried crossing these males to
dow/FM6 females, but got no progeny.

I then crossed heterozygous females individually to FM6 males (different
balancer stock, balancer lacks w and ct).  I looked for male offspring that
had the mutant phenotype.  For every cross, all white-eyed male offspring
had the mutant phenotype.  I established stocks by crossing heterozygous
females to FM6 males.  In these stocks, all white-eyed males have the mutant
phenotype; I never see white-eyed females.

The fact that I got no offspring from crosses with mutant males, and that I
don't observe homozygous mutant females suggests to me that mutant males are

Mutant males also seem to have reduced viability.  In my experiments, I need
to collect adults immediately after eclosion.  To do this, I collect
prepupae and maintain them in a Petri dish on moistened filter paper until
the day before eclosion.  I can select mutant flies, because they have white
eyes.  Mutants are transferred to a collecting chamber, where they are
monitored until they eclose.

If I collect 50 prepupae, I expect that about half will be males and that
half of all males will be mutants.  So I should get 12-13 mutant males.  I
actually observe far fewer, usually 4 in 50.  I also observe an unusually
large number of dead pupae.  I believe that most of these are mutant males.
Death usually occurs after head eversion, but before the orbital and ocellar
bristles and vibrissae become visible (between Bainbridge and Bownes' stages
P5 and P10).  Mutant males that do eclose appear perfectly healthy (but not

So what is going on here?  Why are mutants previously described as viable
and fertile now semi-lethal and infertile?  Is there anything I can do to
increase viability, or is this something that I just have to live with?

Any explanations or insights would be greatly appreciated.

Yours truly,
Gae Kovalick, Ph.D.
Assistant Professor of Biology
Department of Science and Mathematics
University of Texas of the Permian Basin
4901 East University Blvd.
Odessa, TX 79762
Phone: 432-552-2265
Fax: 432-552-3230
Email: kovalick_g at utpb.edu
Web: http://www.utpb.edu/scimath/kovalick/

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