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Determining ploidy

biosci-request at net.bio.net biosci-request at net.bio.net
Tue Jun 22 17:58:26 EST 1999

Crona O'Conallain asked:

> I am interested in having the ploidy of a polyploid strain of S.
> cerevisiae determined and was wondering if anybody could recommend a good
> method for doing this and a company/institute that could provide the
> service. I was thinking of perhaps FISH analysis but do not know what
> company/institute to approach. All suggestions regarding other methods or
> an institute/company that provides FISH analysis of S. cerevisiae would be
> most appreciated.

If you are set up to do it, you could also use a genetic approach.  
1) Does the strain mate?  If it mates with alpha, it is a, a/a, a/a/a, 
a/a/a/a, etc.  If it mates with a, it must be alpha, alpha/alpha, etc.  
To distinguish among these, sporulate and dissect tetrads from the 
mated strains.  If your original strain was a and you mate it with an 
alpha, you should get decent spore viability with mating type 
segregating 2:2.  If your original strain was a/a and you mate it with 
alpha, the resulting triploid will produce very few viable spores.  If 
your original strain was a/a/a and you mate it with alpha, you will 
make a tetraploid that should give good spore viability and roughly 
half nonmating (a/alpha) and half a-mating (a/a) segregants.

You get the idea.  Of course, if the strain is homothallic that will 
make the analysis messier.

2) the second question you can ask is does your strain sporulate?  
If it does it has at least one a and one alpha allele at MAT.  
Dissect tetrads and determine spore viability--triploids will be very 
low; tetraploids will be higher.  Tetraploids that are a/a/alpha/alpha 
will give rise to a mixture of a/a, a/alpha, and alpha/alpha 
segregants while a/a/a/alpha will give a/a and a/alpha and 
a/alpha/alpha/alpha will give a/alpha and alpha/alpha.

Beth A. Montelone, Ph. D, Associate Professor
Division of Biology, Ackert Hall
Kansas State University
Manhattan, KS  66506-4901
phone (785) 532-6092; fax (785) 532-6653
web site http://www-personal.ksu.edu/~bethmont

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