h 26, 1952

| Bear Tom:

ZI juet recalled that you hed mentioned some experiments on the stimulating
effects of light on K-12 recombination.

T was just about to set up some such when I remembered this. The F-story
fa ranifying indefinitely, It seens to be feasible to set up a sexual—potency
qvatient between the genetic P- and Cavalli's Hfr as axtremes. Cultares of
approxizately the same grade are relatively infertile ag compared to sexier
combinations. Porfians aore igterasting, the gratisnt series can also be used
to rationalize the polarity of segmental elimination in the persistent, head-
aygous (for Mal and §) diploids: the elimfnution usually occurs in the ehrome~
some from the relatively F+ parent, This would account for the reversal of cer
tain linkage relationships in orosses such as 53-861 x 4-1177; 58-161 x WLlL77¥e
and back again with 58-161 Afr x %-1177 ¥+ (or F-).

Relative? sexuality immediately brings to aind the Hartmann-Knlep-ibewus
stories in various algae, and from there 1t 1s a brief step to ii lumination
etuiles. It occura to me that you may indeed have the "texas" effect, but that
this itself fs an artefact. I myself have had rather poor luck in duplicating
the effect (except erratically), probably because I wae foolish enough to use
a low preseure 2637 lamp, while they seen to be fond of a high pressure, poly-
chromatic source. J intend to repest it now, but I wonder if it would be asking
too mich to have the details of your experiments. Our F+ series makes it poe~
sible to plan the experiments on a concrete working hypothesis,

In your fellowship applications, I hope you did not commit yourself to
etert later than next September, hile this aay be necessary, Y may have been

Sincerely,

Joshua Lederberg