December 23, 1955

Dear Dr, Barricelll

Thank you for your note suggesting cer tain experiments. However, I have

to tell you that there is a misunderstanding concer the output of

crosses 1 and 2, which you quote from our 1953 paper, (our crosses #7 and 8).
At this point in our diseussion, we did not distihguish the different {mune
phenotypes: the term "parental" means, simply, the reactions to lambda. It
would not he possible to distinguish the phenotypes of Lp’ Ip2” and Lp) Lp",

excapt by testing the lysogenica with lambda-2. This was actually done, ant

I gan assure you that all the combinatiof are found. The detection of the
various genotypes has been greatly facilitated by a wife's more receht finding
that Maly; and Lpo are the same locus. (See enclosure}. The same tgpe of classi~
ftention has bean applied to cross 8, und again sll the combinations hawge been
fouhd. Sama of the crossea have been made with Hfr x F- te preclude the possibi-
lity of interfering 7: infection during the cruas.

If you would like to verify these points for yourself, I will be happy to
gend you the necessary stocks.

Similarly, normal segregag$ion for Gal is found regardless of .whether the
F- parent (in crosses of Hfr x F- as well as Ht F+ x F~) is Lp, or Lp,f.

Jacob and Wollman, using a stock of Hfr which has somewhat different
properties have found that, in the cross Hfr Lyo* x F- Lp’, most of the zygotes
are lost by the syngamic iniuction of the Lp+ prophage. This is also associated
with the alteration of Gal segregation. However, this effect is independent
of tha whether or not the F- parent 1s Immune-2 or not. rm With our stocks,
the polarity for Lp has little or no effect on Gal segrem tion, and the Lp.
matation has none.

As 1 have indicated earlier, I do not see why you should stress the applicabi-
lity of your genophore hypothesis to K~12 crossing, when it 1s so well exemplified
by transduction. On the other hand, the K-12 sexuality is so sharply different
from transduction that I am reluctant to see the two confused with one another.

With best wisihes of the season, Yours sincerely,

Joshua Lederberg
Professor of Genetics

Dr. Nils Barricelli
Riilebakken 15
Oslo, Norway