Re: can environmental variables induce visible mutations in fruit flies

Dear Daniel,

     There are many mutations in fruit flies (Drosophila) that are
visible with a good magnifying glass or microscope.  The database
of Drosophila is called FlyBase, and it is located at this Indiana
University www site:  http://flybase.bio.indiana.edu/ From this
"home page" you can find information for any level of fruit fly
research, from "beginners" to molecular cloning.  There is an
on-line tour called "The Interactive Fly" at:  http://flybase.bio.indiana.edu/allied-data/lk/interactive-
fly/aimain/1aahome.htm 

     A link from that introduction can take you to pages
with drawings of common fruit fly mutations: http://www.exploratorium.edu/exhibits/mutant_flies/mutant_flies.html

     There are many different types of "mutations" with many different
causes.  In the early years of genetics, people did not know what 
genes were or what they were made of.  We now know that genes are 
made of DNA and a "gene" is any segment of DNA that causes or influences
a trait in the organism.  The most common type of gene is a segment 
of DNA that is transcribed into a messenger RNA and then this messenger
RNA leaves the nucleus and is translated into a protein (an enzyme or
a structural protein) in the cytoplasm of the cell.  Other types of
genes encode functional RNAs such as ribosomal RNA or transfer RNA.
There are other types of genes too, but these are the most common.

     A "mutation" is any change in the DNA that changes the function
of the gene.  One type of mutation is a change in one of the DNA
bases (called a point mutation, because a single point in the
DNA chain is changed) which then changes a single amino acid in
the protein, or destroys the start codon, or creates a stop codon
in the middle of the gene, or disrupts the function of the gene
in some other way (for example preventing transcription or
splicing).   Another type of mutation happens when a whole segment
of DNA gets moved.  This includes chromosomal translocations where
one end of one chromosome gets swapped for the end of another
chromosome.  It also includes what are called "transposons" or
"jumping genes" which are segments of DNA that mover from place
to place in the genome, often times landing right in the middle
of a gene, and destroying the function of that gene.

     If a mutation is very rare, it can be almost impossible for
a single researcher to find it by looking at wild-type flies that
have been exposed to strong mutatenic agents such as radiation or
mutagenic chemicals.  So, for example looking for the curly wing
mutation:  http://www.exploratorium.edu/exhibits/mutant_flies/curly-wings.gif
even though this mutation is dominant, (only one copy of the gene 
needs to be mutated), starting with wild flies, is difficult.

    For that reason, geneticists have come up with all sorts of
clever tricks for making it easier to find rare mutations.  They
have stocks of mutant and wild-type flies that they share with
other researchers.  One trick is to start with mutant flies and look
for the back mutation.  This works great for something like curly
wings, because the mutant winged flies can't fly very well at all.
So it is real easy to spot one wild-type back mutation among 
thousands of mutant flies.  You don't have to look at each of the
thousands with a microscope, you just look to see if any are
flying.

    Environmental changes, such as changes in temperature or changes
in the acidity of foods, can possibly change the frequency of
mutation (especially transposon mutations and chromosomal translocations)
but only by a small percentage.  So if the normal mutation rate of
curly to wild-type is one in 100,000 the mutation rate at the 
high temperature might go up to one in 50,000 or something like that.
Starting with wild flies and looking for different shapes or
eye colors you would see variations in the population due to 
many genes (just all sorts of hair color, height, weight, eye color,
curly or straight hair, are "normal" for humans, so too are there
many different variations in fruit flies that would not be caused
by "mutations" that you are looking for).

   Rather than looking for mutations in wild flies, a good starting
place to study fruit fly genetics is to order stocks of two types
of flies (such as white eye and red eye) and learn to breed them
to tell if the trait is dominant (Is red dominant over white?) 
or recesive (If red is dominant then white must be recessive.)
or co-dominant (white crossed with red makes pink-eyed offspring,
then pink crossed with pink makes white, pink and red in a 1:2:1
ratio.

   Genetics is a very interesting an exciting field to study.  But
it can also be very frustrating and not exciting if the experiments
are not planned right.  It took hundreds of very hard-working people
working for hundreds of years to learn all we know about genetics
today.  There were many failures along the way.  Science is much
more exciting today than it used to be, because we have so much
better communication.  There are www sites and journals and textbooks
about every type of research.  There are databases and stock centers
that supply research materials.