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NATIONAL RESEARCH COUNCIL
CANADA

ENERGY PROJECT

CHALK RIVER. ONT.

April 22, 1948.

Dr. Joshua Léderburg,
Department of Genetics,
University of Wisconsin,
Madison, Wisconsin,
U.S.A.

Dear Dr. Lederburg:

You will doubtless remember having mentioned last
Christmas your observations of sectored lactose positive-lactose
negative colonies from irradiated E. coli. Evidence from such
material would seem relevant to a study of "delayed effect" of
irradiation which I have just completed, and I would be interested
to know whether you have done anything further along these lines.

My own preliminary results using mutations from
B/r to B/r/l indicated that delayed phenotypic expression alone could
not explain a delay of twelve generations. This left two possible
interpretations: (a) delayed mutation, and (b) delayed division of
induced mutants, plus delayed phenotypic expression. The evidence
is now pretty conclusively in favour of the second of these.

If there is no delayed mutation then your sectored
colonies would indicate the presence of two or more nuclei (or other
forms of gene reduplication), and there is just a possibility that
delayed phenotypic expression is the result of such reduplication,
although I think it unlikely. For this reason I would be interested
to know whether you are doing anything further with your materials.

Tam sorry not to have got off to you the reprints
of the chromosome and chromatid interference studies which you
requested, but have been unable to locate them so far. Huskins is
unfortunately down to his last few copies.

With all best wishes to yourself and Mrs.
Lederburg.

Yours sincerely,
phan |S? foceerda

HBN/iml H. B. Newcombe.