Maroh 26, 1954.
Dear Bruce:

Thanke ever so much for writing so detailed an account as your letter of
the 16th. You may have found my last letter (March !) rather puzzling, with
ite account of some of the micromanipulations here, if you did not keep in mind
that the last I had heard frou you on these was several months ago, and at that
time all you had to say was that there was an apparantly irregular pattern of
replication. Reading your most recent letter, I am in fact astonished (and de-
lighted) at how closely we had converged, on such technical features aa the
trapping-drop for isolation, all the way through the experimental details, and
finally including tie “polyteny" interpretation! The latter is especially grati-
fying, as I thought this at first a rather wild idea, but if we have both fallen
dato it, essentially independently, there may be something in it.

As I see it, icragular replication can of course account for the resulte in
an ad hoc way, tut does not seem to suggest any further directions, and ff for
thie reason only ought to be adopéed as a last resort, I can see no occasion
for phenotypic lag in the usual sense, if enly that observations on mbat semb-
clonal lines show an dumediate and precise delineation of notile from non-motile
daughter, and because the apparent Garryover 1a seen only in early, never (7)
late generations. If the multiple semiclones tesult from divex division, ieee,
partition rether than replication, without multiplication, we can then enquire:
what Le being partitioned? Bx hypothssi, the particles do not reproduce in the
transformed celle. Were they all genes in the donor cell, the reproductive capacity
having been lost as an accident of transduction (abortive transduction iiypothe sis)
or were they non-reproducible particles in the donor cell itself, hee., the
hypothetical immediate products of gene action. The latter notion might be more
easily reconciled with pedigrees likes 1¢-99a etc. I.E, I would expect the poly-
tenis status to be more or less wniforn from one donor to another, and tot to
be profoundly disturbed by traneduction, and not to reach immense values, while
the extent of accumulation of particulate, non-reproductive gene products might
be expecte? to be lees umiform.

Like yourself, I have had a few rather diatur bing pedigrees showing either
very manysemi-clonal celle (-7 100), or division ‘occurring wuite late in a given
pedigree (wy latest 1s not earlier than the 14th, while yours must have been
in the neighborhood of 20 to 25); on the other hand, I have carried one semi~clone
to the th generation, in a pedigree where no further division wus seen after the
10-14th generation, so there is certainly a clear distinction between the early
and late behavior of the "particles", so clearcut as to seem “somekow contradictory
to the iden of irregular replication. I admit both processes ray operate, but do
not like to multiply hypotheses, and &f we admit this it can shoulder the whole
burden itself. But like yourself, I have found nost pedigress to show quite
limited"replioation! generally completedwell before the 10th generation, and
often much earlier, So there is actually very little disasrearent between us on
experimental findings; I hed no idea you had gotten so far, and it ics quite start-
jing to see the concordance,

The only point where I do demrt from your account ic the cerregation of
non-motiles from swarm-equivalents. I do not have very many of these, aa they
are quite infrecuent in my material (and none yet have turned out to be the
complementary crose-overs I wae tmitially searching for), but ot least hakf the
"swarma" have been aseécieated with non~motiles. I think the difference might
be due in part to my use of lag phase cells, from which motiles appear in about
2 houre et room temperature, 1.62, at about the first fiesion. My material is
now entirely SwW- ~-x SW~666, and I have had very littled trouble with lysis, ete.
The lower temperature may have something to do with it. S¥- x—~ SW-666, on the
other hand has been very discouraging: low yields of motile individuelo, and
low viability of them when found. The other thing is the single instance
not yet repeeted, of a motile clene and numerous semiclones frer one individual.
If thie should ever be found from a late generation, we might have to accept the
irr, repl. hypothesbe after all, and would certeinly have to reject "zene products".

In re mapping, I understand your argument now. I don't know what to think of the
first postulate, that am overlepping entire segment is always traneduced in the
first inetence: these experiments may provide the evidence for it. Lerry and Esther
have been setting up various trials on this point with the K-12 traneduction, but
no decisive ty¥¢7d/dp results. At least a fair fraction of the lambde particles
would, however, heve to carry at leaet two loci, judging from tranaductions to
double Gal- rutente, but whether this in true of moet or all ie not yet settled.
Mapping is, if anything rather more difficult here (on the ,teneductions, not the
recombination enelyeis) ewing te the interim "heterozygous" cobdition.

In your analysis, you are I take 1+ ignoring doub'e crossovern completely. I wonder
if they would net complicate the picture, especially for the qualitative approach.

I think it still absolutely essential to make quantitative measurmmen&és on the
incidence of single and doubles, although one cannot, of course, directly compare
different systems (C£., @egs, SW-666 x-- TM2, and SW-666 x-- SW-623). The comparisohs
of Fle,” --x... with Fla,” --x... seen to me by far the most reliable evidence,

if done quantitatively. Without counts, once cannot aeseee the statistical signifi-
cance of the assertion that 5AS --~ 26 gives no déiXea/ singles, es compared with

SuSPL a” ~~ 28. But a story like this often hangs on its whole convulatency as
moh as on the rigor of ite details.

As to publication, you can of course quote anything you like that way seem useful.
But I can hardly join in the authorship of your projected paper on the mapping,

as I have done nothing conetructive on it thet is net already in print. But may I
make the counterpropesal of such an arrangenont for an ultimate definitive account

of the cell pedicrces? I am sure both of us will want to talk ahout it to sharpen

our ideas; I hope before we go tco far out on the limb that j@f one or both of us

can think of some more decisive uxperimente to choove anong the hypothetical explama-
tions. If nothing else, it seems to me that the concordance of results on several
systems has been indispenanble.