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tetrad ratios

Charles N. Cole Charles.N.Cole at DARTMOUTH.EDU
Fri Dec 3 17:02:55 EST 1993

We are trying to prove that we have cloned the gene which is ts in a mutant
strain of interest.  To this end, we've taken a fragment from the region of
the gene (the fragment covers the 3' end of one ORF and all of two other
ORFS) and inserted the fragment into a URA3-YIp plasmid.  We linearized
within the inserted fragment from our clone and transformed and isolated URA+
colonies.  We made this insertion into both the ts mutant strain and into the
wildtype parent.  We then crossed the ts mutant with the YIp with wt;
separately we crossed the WT with the YIp and the ts mutants, made diploids,
sporulated, dissected tetrads and scored them.

In one cross, we got 25 PDs and 1 NPD, which is probably okay.  However, in
the other, we got 24 PDs and 13 NPDs and no TTs.  Has anyone out there seen
any similar sort of unusual ratios like this?  Does anyone have any
suggestions as to what might be giving this result?

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