How Do They Keep The Strain So Pure?

Chris Jones & Deirdre Sumpter 4drjones at usit.net
Wed Apr 29 00:50:39 EST 1998


In article <eeeEs5Ewo.6Dy at netcom.com>, eee at netcom.com (Mark Thorson) wrote:

> I've been keeping vestigal-wing _D._ for several months now,
> must be around 15 or 20 generations, starting with cultures from
> CBS.  A few generations in, I noticed one fly that flew out
> from a culture vessel, and currently all my vessels are
> contaminated with fliers.
> 
> I'm wondering how CBS keeps the problem in check?  Do they
> screen for vestigial mutant at each generation?  

Call CBS and ask them.

> I'm considering
> dumping all my cultures and starting over, but would the
> problem re-occur if I'm running open-loop (i.e. no screening)?

I don't know, but it wouldn't surprise me. My guess is that there is a lot
of evolutionary pressure in favor of flight, and particularly with large
populations, you'll see the occasional "flyer." This is a constant problem
with mutants in genes affecting learning and memory (my area of relative
expertise). Even if the smartest ones in the population are only a tiny
bit smarter than their sibs, they succeed marginally better, and this
effect snowballs over generations.

One solution may be to use an isogenic population, so you have removed all
the little genetic variations in the population which serve as "raw
material" for the selective forces. This procedure is not for the tyro or
dilettante, however. (Not to say that you're either, it's just a
not-insignificant effort.)

Alternatively, you could select every 5 or 10 generations, which shouldn't
be all that difficult. Another option would be to construct a strain with
multiple defects restricting flight, so that the chances of simultaneously
accumulating modifiers for all of them would be that much smaller.

A more prosaic explanation is contamination by flying outsiders....

> For anyone who remembers my earlier post on the subject,
> my culture vessels are an outstanding success:  cheap,
> easy to make, easy to use, and very productive.  My attempts
> at engineering a new culture medium have been barely
> workable, the biggest problem being mold.  Sometimes I lose
> a whole batch to mold.  I may go back to 4-24.  Does anyone
> offer a cheap substitute?  If so, contact information please.

FWIW, I'm in Nashville, and 4-24 has proven completely incapable of
stopping the molds here, at least in some culture vials. In a given batch,
I'd have an apparently random 5 to 10% of vials completely overgrown by
mold within a few days. Very frustrating. I'm now using the older
Bloomington recipe (agar, molasses, cornmeal) with Tegosept as a mold
inhibitor and have had far, far fewer problems. There are a number of
recipes I've seen, almost all of which use this to fend off mold. This
could prove to be a real problem for you, I'm afraid. Unfortunately, Sigma
Chemical (at least) won't ship to non-business addresses; perhaps they're
afraid someone will succeed in using the stuff to blow up a government
building.

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