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embryo viability

Emma Rushton rushton at biology.utah.edu
Tue Feb 24 12:18:29 EST 1998

In article <34EC5E6C.7450 at HAWAII.EDU>, Anne Wheelock <wheelock at HAWAII.EDU>

> Hi Drosophila workers!  I have a question concerning embryo viability
> that I hope one or more of you will know the answer to.  After I have
> collected embryos on an egg-laying plate, and allowed them time to
> hatch, I count egg cases and unhatched eggs to determine viability.  The
> majority of unhatched eggs are white; a small minority are brown.  I was
> told by a resource here to consider all the white ones as unfertilized
> and the brown ones as fertilized (and obviously dead).  I'm not
> convinced that all the white unhatched eggs are unfertilized - some are
> homogenously translucent, some are clear at the poles with a clump of
> white in the middle, etc.  Most are covered by the chorion so one cannot
> see into the egg.  Does anyone know how to tell, using a dissecting
> scope, whether an unhatched 36-60 hour old embryo is fertilized or not? 
> Are there some visible changes inside the embryo that would be clues to
> whether it is fertilized or not (again, at the dissecting scope level)? 
> THANK YOU!  my e-mail is wheelock at hawaii.edu.  Anne Wheelock

All the fertilized eggs will turn brown if you leave them long enough, but
there is a quicker way to tell. Take a fine hypodermic needle and puncture
the egg.  If the egg turns into a pool of liquid and jelly it is
unfertilized.  If you see some structure in there, it is fertilized.  How
much structure you see depends on the mutation.  In my hatching
efficiencies it is easy, because I expect to see cuticle and denticle
belts.  Other mutants may be harder to distinguish from unfertilized.


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