H-168, Lacv.Xylv.Mtlv. etc., has been recovered from the cultures you lately sent, and by now you must have received a copy
which has been mailed to you. We tried to reproduce the loss of Xyl+, but in several hundred tests, every Mtlv has been Xylv.
The presumption of a second crossing seems to be most likely, but unprovable. I wonder how much of the work on H168 depended
on the persistence of the Xyl-? As I have lately been trying to think about it, your single-cell work was directed as answering
several questions: a) that single cells so segregate, certainly proven beyond doubt. B) whether the aberrant ratios could
be explained by lethals -- very likely, but not directly provable because (probably) of multinucleous cells. C) whether there
are two or four strands, and whether segregation occurs in one or two divisions -- the answer to this is a little uncertain,
because the previous heterozygotes had one type of segregant so predominant. H-206 should be a superior stock for answering
this question, because the 3 classes which do occur are so nearly equal in frequency. I can't yet answer your question
about H-206; if you are having trouble reisolating it, let me know and I'll send you another stock. I don't know what
else it is heterozygous for.
If you've gotten back to work, let's discuss what's next.