March 6, 1955

Dr. J. G. Ross

Dept. Agronomv

So. Dakota State College
College Station, 3.D.

Dear Dr. Ross;

I have been following your reports on genetic effects of colchicine on
Sorghum with som interest. This is now only slightly more acute as I am
starting to prepare a monograph on "genetics and chemotherapy" and may
try to include soms comment on diverse genetic effects of chemical agents
such as colchicine. Unfortunately, my interest is not matched by my infor-

mation, There are several points that may very well be presented in your AS
papers, but I may have overlooked or failed to assimilate. Would you, as 7
ag aort of personal favor be willing to answer some questions? I would €A
also be in your debt if youncould send m your reprints as well. ~
First of all, I am not entirely clear as to the overall design. I gather 4
that a number of plants were treated, others left alone, and that these
were then selfed. Altogether, how many runs gave there been? How many U and «*

C plants have been subse uently followed’ Do the conditions of treatment
preclude any possibility of “introgression"?-— or have you some specific
markers that would serve this end? If the experiment has been repeated, how
reproducible is the result? Are the mitants picked gp in C, possibly the
result of selfing of heterozygous mutants, or are they too brevalent already
in C,?

1

The second question concerns the genetic analysis. I gather that your cytolo-
gical studies of hybrids now rule out the likelihood that the mtants repre-
sent new karyotypes. Is it possible, however, that there are two chromosome
pairs (say A,A, Aj A>) in the standard, such that A, and Ay already show con-
siderable homology, ao that the mtants might be A,-tetrasomic, Aj~—nullisomic?
I did not notice any segregations from backcross ickghis hybrids—— fas there been
a second backcross generation to verify that recessive mitation(s) are involved?
If not, would 1t be worth while considering the possibility that the manifold
effects are cytoplasmic, in which case the next generations from reciprocal
backcrosses would differ?

I hope these points dco not seem unduly naive; I can only apologize for them
by the fact that my own special material is somewhat far afield from crop plants.

With best regards.

Yours sincerely,

Joshua Lederberg
Professér of Genetics