January 27, 1952

Dr. T. C. Nelson
Biclogy Danartaeant
Vandervilt University
Nashville, Tanneasee

Dear Tom:

z Just remembered a detail I forgot ic emphasize in previous letters.
Esthar coi I are going to do cur best not to stay hore cver the summer,
In any event, 1t would be preferable to discuss your plans in terms of
a beginning date here not earlier than next September. If you could arrange
comfortably to start next January it might be better yet, but we can digs—
cuss this extremity at Cinncinnati.

We've lately run into a remarkable lead on fertility in K-12, There is
& genetic factor "F+" required in at least one parent for crossability.
This factor seems to be tranamitted extra-cellularly with high efficiency.
Only a few stocks in ordinary use have been F-, but we are finding ways
of inducing the loss of F+. Yore ag Cinn.

Sincerely,

Joshua Lederberg