INDIANA UNIVERSITY
BLOOMINGTON, INDIANA

DEPARTMENT OF BACTERIOLOGY January 26, 1919

Dr. J. Lederberg
Department of Genetics
University of Wisconsin
Madison, Wisconsin

Dear Lederberg:

In the first place, I have agreed to collect the material for
the Section on "Genetics of Microorganisms" in the "Methods in
Medical Research". Can I hold you to your promise to prepare the
part on Procedures for the Study of Biochemical Geneties and
Recombination Phénoména? You told me you could have this in July.
As you know, the main thing is a detailed description of the
methods used in those typical experiments that are likely to be
used by new people working in the field.

In the second place, a poor experiment of Miss Kann gave me
an idea which we have been unable to prove, but which you may
easily disprove.

Suppose K-12 cells are all of mating type A, but give rise to
a few mitants of type ae In a mixed culture, these could mate with
other types of cells and give recombination. This "mitation" theory
would account for the frequency of recombination, for the fact that
the proportion of recombinants in a plate goes up slower than with
the uare ,of the number of parents, for the increase in recombina-
choke tite tend Ghee, for the fact that the number of recombinants
depends very little on time of contact. We tried to test that by
seeing if presence or absence of prototrophs in liquid was onky a
matter of the number of parent cells (same number in different
volumes). It does not work: there are more prototrophs in smaller
volume, although the frequency is not dependent on concentration
only. Other kinetics tests, like fluctuations, would be tiresome.
You can test the possibility using your recombinants and backe
crossing them. Even if my suggestion were correct, you may not find
equal numbers of prototrophs of both mating types, since the proto-
trophs of type “a” may have a chance to outcross again after being
formed, and become deficient again. In agar, however, this may be
rare. Also, you can devise experiments with suitable stocks to get
both recombinants from a cross, particularly with the heterozygate.
This should be the answer to the question. Let me know if you
already have pertinent evidence; if not, can you test for it?

Best regards to you and Esther.
Yours,
Karr“

SEL:VB Ss. Ee Luria