McClintock briefly answered some questions Stern had asked regarding a series of phenotypes in maize and then related some
findings from her most recent trip to Mexico.
Number of Image Pages:
2 (173,264 Bytes)
1960-02-14 (February 14, 1960)
Original Repository: American Philosophical Society. Library. Curt Stern Papers
Reproduced with permission of the Curt Stern Papers, American Philosophical Society.
Medical Subject Headings (MeSH):
Searching for the Origins of Maize in South America, 1957-1981
Box Number: 3
Folder Number: 3
February 14, 1960
I found your letter of February 3rd on my desk when I arrived at the laboratory yesterday after being in Mexico for several
months. In it you asked the question: Is there a series of phenotypes (in maize) so that 1-2-3 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
associated with the development of anthocyanin pigment-- the C (color in aleurone layer of kernel) and I (inhibitor of anthocyanin
expression) alleles-- that are clearly quantitative in that additions of a particular allele build toward the normal phenotype.
Each addition of the allele adds a definite quantity of the substance that is responsible for the "normal" phenotypic
expression. This may be illustrated by the wx alleles.
In the endosperm of the kernel, which is triploid, the "normal" phenotype is characterized by the presence of 28%
amylose starch, the remainder being amylopectin. The basic recessive allele, wx, or a deficiency of Wx, 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 wx/basic wx) will produce 20% amylose in two
doses and 28% amylose in 3 doses. In other words, with increased loses of the allele, the normal phenotype is reached.
The C-I series is another example. Increased doses of C increase the amount of anthocyanin pigment that is developed in the
aleurone layer of the kernel. By means of duplications, it is possible to obtain kernels with 6 or more C alleles. I, on
the on the hand, inhibits the production of anthocyanin in the aleurone layer of the kernel. Sometimes, I/C/C kernels have
some color in the aleurone layer but none is seen with I/I/C constitutions. However, by means of duplications, it is possible
to get constitutions that are I/C/C/C/C/C. Often, the presence of I is not detected in the kernels of this constitution.
There are other allelic combinations of similar type but I hope that the above may serve your purposes. Also, I hope that
this does not arrive too late for your purposes.
It is good to get home again after two months of intensive work in Mexico City. During the past two years, I have spent a
lot of time in Latin America and it looks as if I will be spending more time there in the future. I have been working
with the maize group in the Rockefeller Foundation in helping to trace the origins of races of maize found in the Americas.
My job has been to examine the knob constitutions of the chromosomes of plants of different races and by means of the particular
combinations of knobs, to determine the origins and migrations of the races. I started doing this as a "contribution"
to our Latin American re1ationships but it is proving to be quite interesting as a piece of research. Surprisingly enough,
the knob constitutions of the chromosomes in the races are excellent indicators of these relationships. Also, it looks now
as if a knowledge of such constitutions may serve to select those races that should be used for future improvement of commercial
maize. The Rockefeller Foundation is anxious for me to take over the job of further analysis of South American races. Because
of the possibility that extended study may illuminate the origin of maize, its migrations through the centuries, and also
because it may give us a means of selecting those plants that may be potentially successful in given areas, I am tempted to
continue the study.
I have had very little news of you and the family recently. There must be some interesting news, too. I do hope that all
has been well with each of you.