August 1, 1955

Dr. M, Dewerec

Department of Genetics
Carnggie Institution

Gold Spring Harbor, L.I., N.Y.

Dear Dr. Deneree:

I have only just now had epportunity to see your paper in the Proc,
of the 9th Int. Congress of Genetics, A small error erept into your account
that I think you would want to lmow about, for the record, Tt concerns the
genetic control of phage resistance,

In my 1947 Genetics paper, I mentioned at least three Tl-resistant pheno
types, As T believe is clearly implied there, these are distinctly ponewaliclic,
In particular, the */1" types have always been definitely et different loci
fron the "/1,5" types, There may be more then three loel, but there are at
least three, which show several percent of recombination among them, Unfor
upnately, in X12 (as pa spontancous mutants) we never did Find any volncidentay
auxotrephss: I would be willing to bet} that these are non-allelic to the others.
However, my wife has recently found that Ips” Is the sams mmibation as Mal,” this
is resistance to lembda-2 phage,) I an looking forward te receding Brysonts
comment on the seme topic,

With regard tam to plelotrepy at the S locus, I must of course agree as to
the allelism of the S™ and s4 mutants that have been intercrossed so far, I az
less convineed that the other effects are at the same locus , whch requires 2
backcross test that has not, I believe, so far beon reported, 8° mutants, especial:
are subject to considerable selective pressure while they are being isolated and
carried, aid I suspect they accumulate many additional mutations in the coutse
of handling

To return te the Tl-resistance, one apparent case of pseudoallelisn turned
up thera, and was the basis of discovery of a nondisjunctionul heterezycote, as
reported in my 1949 (PNAS) paper. IT have not studied y,P x V,7 " very extensively,
but have not found any recombinants in some hundreds of tests? The hetebo ay yous
compound was, however, sensitive to TL, so that there is no ole-trans position
effect in this case,

Yours sincet’ély, “~~

Me

Josnue Lederberg