daly 22, 1955

Deay Tom:

Thank you for your letter, ani the data on the cultures. The story
seeme now pretty clear cut these modifiers have been cresping in st
everywhere ani have to be locked out for very carefully. Esther has some
definite Galy- hemizygotes from another cross.

Jacob ani WOllman sent us the uss. on the “partial transmission” about a
week ago. Our comment was the same as yours, even to "coltus interruptus! *
Theye own date seem to point pretty definitely to an aterilution cf the
altered segregation frequencies as a direct result of the treatment— the
majer Glass of recombinants levels off, and it is the incidence of Galt, otc.,

that continues to rise. If he is dealing with one linkage group,
as he implies, then one end of each chromosome mast already have entered early,
andi would do so in entirety (late Dbleniing) if it were left uniisturbed. This
would be partioularly interesting if one conld be sure that this was partial
fertilisation, Unfortunately, one still cannet say from theso experiments
whether the ganetic prommoleus has been broken in transit, or whether its
pairing properties have been altered so as to changg the crossover pattern.
A reduction of specific pairing ( a la Gavalli & Jinks) would have the sane
effe et of accentuating the bias in favor of the F- parent. Someone ought to
repeat the Blending technique in connection with diploids te try to leclate
the anouploids that would clikch the partial-fertilisation theory. Alternatively
that technique might be applicable to higher organisms toc.

In re Demerec linear seguents, I have not yet seen enough data to be absolutely
convinced of it, and am somevhat muspioious of the shor$ceuts that they have been
using to seore types (i.e. ly differences in count on various media, Pather than
specific characterisation of individual isolates). It 1a hard to see how thay
eould be off on the fact of linkage (regardless of sequence). I had a structural
notion too, not quite like youres:: the anabolic enzymes are integrabed onto a
linear structure which corresponis t@ the chromosomal sequence. The mutants ths
Demeret looks at are not defects in the enzymes per se, wut in the eltes to which
they nermally attach. If he examines more mutants, he may find some unlinked thtt
are seenitely functionally equivalent to some that are., unless there is enough
polymerism in Salmonelia to vitiate that search. At any rate, I'd want to ask

whether very many tryptophancless, for example, have been isolated ani gl), found
a $0 ve part of a single segnent.

4 > Wa whl be delighted to see you if pou can drop by. Our house is still therey
Ske “ bat the grounds may be unrecognisable. Hveryone around the lab. is well (except for
qb * Ly the heat). Larry is vacationing Wiefly in Colorado, @aylen ani I have been 1eo-

lating hyphal bits for clinching evidence on heterokuryosie in Streptomyces-~ there
4s no doubt about it; so far nothing more interesting.

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