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Viability of diploids vs haploids in pombe

S L Forsburg forsburg at nospam.salk.edu
Thu Jan 16 07:58:45 EST 1997

Karen Yoas wrote:
> Read in Experiments w/ Fission Yeast that diploid cells are less viable
> in haploids.  Why?

Well, I can speculate....

think of the usual pombe cell cycle.  These guys don't WANT
to be diploid, they want to be haploid.  The diploid phase is
normally transient, a brief stop on the way to meiosis. Unlike 
cerevisiae, pombe diploids do not shut down mating functions
 or haploid specific genes. If you maintain the diploid in the
 lab, you are forcing a cell that is poised to go into meiosis,
that has most of the signals saying "go", to stay vegetative .
  Metabolically, it is geared to exit mitotic growth.  Look at
them crosseyed, and they sporulate.  Keep them around too long,
and you select for mutants that lose the ability to sporulate
(which is why the pombe lore suggests that you make your
diploids fresh when you need them, and don't keep them
around in the fridge.  Streak out a diploid from the freezer
and you often find they are sporulation defective too.)  In
short, the diploid is a cell that in the wild probably almost
never exists.  

-- susan, an a-fission-ada ;-)

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S L Forsburg          forsburg at salk.edu
The Salk Institute    http://flosun.salk.edu/~forsburg
La Jolla, CA

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