CARNEOIE INSTITUTION OF WASHINGTON
DEPARTMENT OF GENETICS

I'eLruary 14, 1960

Dear Curt:

      I round your letter of 3'ebrual.y 3rd on my desk when
I arrised at the laboratory yesteruay after being in Mexico for
several months.   In it you asked the question: Is there a series
of phenotypes (in maize) so that l-Z-3 doses build up toward
normal?

           There are alleles associated with the development of
       starch -- the wx alleles (waxy), and the su (sugary) alleles--
    and others associted with the developmen??of anthocyanin nigment--
    the C (color in aleurone layer of kernel) and L (inhibitor of
     anthocyanin expression) alleles-- that are clearly quantitative i.n
     that additions of a particular allele build toward the norms.1
     phenotype.   Each addition of the allele adds a definite quantit::
     of the substance that is res-bonsible for the "normal" rjhenotypic
      expression.  This mag be illustrated by the wx alleles.

       "normal"  In the endosperm of the kernel, whzk: is triploid, the
          phenotype is charac$erized by the presence of 289 amylose
     starch,  the remainder being amylopectin.   The basic recessive
     allele, wx, or a definiency of 5,  results in the absence of
     amylose starch.   We have various alleles, each of which in one
     dose, produces a definite amount of amylose.   As an example, an
    allele that produces 10% amylose in one dose (wx allele/ basic d
     basic wx) will urod.uc?
     7 doreiFY         70% amylo--e in two doses-and ?8 $ ar~ylose in
         In other words, with increased loses of the allele, the
     normal phenotyqe is reached.
            The C-I series is another exarrpie.   Increased 2oses of C
    ?ncre:-tsc the an?_oynt of anthocyanin gigment that is developed in the
     aleurone layer of the kernel.   By means of durlications, !.t is
      Fossible to obt:-iin kernels with 5 or more C alleles.
     other h,tnd,                              2, on the
           inhibits the production of antrocyanin in the aleurone
     layer of the kernel.  Sometimes, uys kernels have some color
>    in the aleurone layer but none is seen with I/tic constitutions.
a    Rowever, by rn;ms of du$lications, it is nossTble to ;:et zonntitutions
IF   th:lt are IJCJwCJgC. Often,  the nresence of I is not detected in
       k'. rnels of t:?:'is conFtitution.                        -

F          There a'e othr;r allelic combinations 3f simi!.sr ty-e but 1
    hope that the above may serve your Turposes.  Also,  !: hope th:2t t+z'.s
    does not a--rive too l.?te for your purpose?.
           It is good to get home again after two months of irtensl.vn
      work in
%        mexico City.   during the past two years, I have spent a lot
     of time in L;2tln .Ir.lcric? and it looks as if I !:rill be spending more
     time there in the future.  I have been workirg ~~?t'? the maize g-ou-?
\  in the Rockefeller Foundation in helping to trace the c>ricins 0-f
         2. 'aces of msiTe fo:and in the ,Americas.  My job h?r,s been to examine ?l?e
  _--.knob constitutionsAof plants of different races and 1)~ m'>l.ns of
          __ _ __
   th.e p`L~~iCV.rar`.~~~bin,~.ti~ns of knobs,  to determine the or'.gins pnd
     migatixv3 of the races.   I started doing this as :a  "contributicn"
    to our Latin American re1ati~~rship.s but it is proving to br quite


interesting a? p. gsece of research.  Surprisingly enough, the knob
corstitutiors of the chromosomes in the races are excellen-
iy-dicators of these relationships.   KlSO,  it looks  now as if 3
knowledge of such ccnstitutions may serve  to select those races
that shol!I.d be used for future improvement:.: of commercial maize,
The Rockefeller Foundation is arxiou? for me to C,-ke over *he job
of further analysis of South American races;,   Eec2use of the
pos35 ~
  Fi!ity -l-hat exteded study may illuminate the origin of majze,
i ts mi.gr5i.t i `J?Iz through the centur;es, and also ber:al;se it rra:y give
us 2 means of select?ng those plants that may be nc7tentlaIlJy
successful in given *7reas, 1 am tempted to continue the study.
     1 heve had very li,tle news of you and the famil.y
recently.   There must be some ?nterestiPg news, too.   I do
hope th-t all h-is been. well :nri.th ee.cl- of you.
              Cordially,