6 ia"

May 12, 1955

Dear Dave:

Thank you for your letter. Esther and I would like to visit you at
Cold Spring Harbor, if we can work it out. However, our plans are still
somewhat jumbled, and with various business ani paranéal obligations, we
won't know until after we're in NY.

The gost probable opportunity would be on Sunday, May22. tie have to
go to Syracuse on an early flight (AA- 10:15) Monday morning; the Airlins
Guide is somewhat confused about this and I haven't found whether this
should be 743 from Newark or 745 from LaG. If the latter, it would be es~
pecially convenient if we could come out Sunday aftermoon * and spend the
night there— but this may depend on whether we can have a place to s&ay,
and the means of getting to the airport the next AM. We will got in touch
with you or Norton or both in NY. We leave Madison Wednesday; you can leave
any message for us with Norton or Ruth Sager at Rockefeller, or possibly at
the Barbizon Plaza Hotel.

As to Hfr crosses, I have to say first that most of my single cell work
has had to be with another system than W-1895 x W-1177; I've been using
a multiple marked strain of another wg line, which is morphologically dis-
tinguishable from K-12, as the F~ parent. I did do a good deal of work with
W-1895 x W-1177, as you know, but not a single sell basis. Crosses here were
diagnosed in three ways: selecting S™ Lac* recombinants on EWB Lac sm-- I call
this sr+ selection; detsoting the phenotypically distinct Lac+Gal+ recombinants
in a setup HfrGal-Lac+ x F-GaltLac- on FMB Lae (which has the advantage of
leaving both parents clive); examining the characteristically sectored Lac+/-
colonies on FMB Lac in #1895 x 91177; a few various others, a.g., Xyl+SR
or Lac+¥,". My conclusions are not greatly different from yours: most (ab. 80%)
of recombinan ta for any markers examined are Lac+S™, or rather are included in
the same colonies which have kawx sr+; there was a progressive decrease in the
recovery of paratypic (from Hfr) markers aa linkage distance increased away from
Lac--— taken together, these facts would iniicate that there is a bias against
the TL end of the Lac linkage group, again présunably a distal elimination
since T and L themselves are so regularly heterozygous in diploids, ‘dumagn and
theke segregation from such heterozygoges is so pebturbed. I am fairly sure now
that the eliminated segments including Gal-Lp, on the one n:d, and Mal~S on the
other are distinct from one another; I haven't definitel,; concluded whether this
TL-linked one is a third, or a manifestation of one of these (if interstitial).

To summarize, for your purposes, the sr+'s (yours or mine) probably measures
most of the zygotes that yield any recombinants at all; it 4s impossible to

measure indepdndently the zygotes that segregate to give on_y

the parentals. In my mating pairs, the incidence of detectable recombinants his
been about 25-30%, but I can't be sure whether the others were all proper zygote.
or not. Hoping to see you in NY,

: oo

¢ / :

Be Bee
fe.

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