November 12, 1948.

Dr. Barhara uaClintock.
Dept. of Genetics,
Carnegie Institution,
Gold Spring Harbor, L.I., N.Y.
Dear Barbarsg

I have just received your letter and scheme for the coli heterozygote.
I haven't studied it yet inndetail, but I habten tc thank you for the effort
that you must have put into it. I will certainly study it very thoroughly.

Unfortunately, I think that I may have misled you concerning one of the
premises: II-3. "the type of crossover chromatids recovered in the the segre-
gants are not the expected ones in that many unusual muitiple crossover
chromatids are represented." I did emphasize that certain multiple-mutant types
could be recovered from the heterozygotes, but they are elusive with respect
to the techniques that were previously available, viz. selectién for protetrophs.
In fact, the multiple mutant types are merely the complezents of the prototrophs,
techniques for the recovery of which had been worked out before. This restatemsnt
does not,I think, alter the bases of your sugvestions, but may require e sonewhat
sinpler version.

Again, I want to thank you for your suggestiovs,
- and remain,

; Yours,

Joshua Lederberg