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OCR for page 211
BARBARA McCLINTOCK
fune ~ 6, Z 902-September 2, ~ 992
BY NINA V. FEDOROFF
BARBARA MCCLINTOCK'S remarkable life spanned the his-
tory of genetics in the twentieth century. Though tech-
nically rooted in Menclel's experiments carrier! out decacles
earlier, the science of genetics began with the rediscovery
of his work at the turn of the century. In 1902, the year of
McCTintock's birth, William Bateson wrote prophetically that
"an exact determination of the laws of heredity will prob-
ably work more change in man's outlook on the worIcI, and
in his power over nature, than any other advance in natural
knowledge that can be clearly foreseen." And indeed, the
science of genetics, to which McClintock made seminal con-
tributions both experimental and conceptual, has come to
dominate all of the biological sciences, from molecular bi-
ology, through cell and clevelopmental biology, to medicine
and agriculture. Bateson's immodest guess was arguably an
underestimate of the impact of genetic knowledge on hu-
mankind.
The chromosomal basis of heredity was aIreacly well
established by the time McClintock began her graduate
training in the Botany Department at Cornell University.
McCTintock made her first significant contribution as a gradu-
ate student, cleveloping cytological techniques that allowed
211
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212
BIOGRAPHICAL MEMOIRS
her to identify each of the ten maize chromosomes. These
early experiments laid the groundwork for a remarkable
series of cytogenetic discoveries by the Cornell maize ge-
netics group between ~ 929 ant! ~ 935. By all accounts,
McClintock was the intellectual striving force of this tal-
entecl group and either contributed substantially to or was
exclusively responsible for many of the discoveries. These
include identification of maize linkage groups with indi-
viclual chromosomes, the well-known cytological proof of
genetic crossing-over, evidence of chromatic crossing-over,
cytological determination of the physical location of genes
within chromosomes, identification of the genetic conse-
quences of nonhomologous pairing, establishment of the
causal relationship between the instability of ring-shapecl
chromosomes and phenotypic variegation, discovery that
the centromere is divisible, and identification of a chromo-
somal site essential for the formation of the nucleolus.
In the years following completion of her ctoctoral work,
McClintock continues! her maize cytogenetic studies, even-
tually becoming interested! in chromosome breakage, mak-
ing important observations on the behavior of chromosomes
lacking telomeres. Using knowledge gained from these stud-
ies, McCTintock cleveloped a methoc! for using broken chro-
mosomes to generate new mutations. Among the progeny
of plants that hacI received a broken chromosome from
each parent, she observer! unstable mutations at an unex-
pecteclly high frequency, as well as a unique mutation that
clefinecI a regular site of chromosome breakage. These ob-
servations so intrigued her that she began an intensive in-
vestigation of the chromosome-breaking locus. Within sev-
eral years she hacI learned enough to reach the conclusion,
published in 194S, that the chromosome-breaking locus did
something hitherto unknown for any genetic locus: it moved
from one chromosomal location to another, a phenomenon
OCR for page 213
BARBARA McCLINTOCK
213
she callecl transposition. The study of transposable genetic
elements and transposition became the central theme of
her genetic experiments from the micI-1940s until the end
of her active research career.
As with Menclel's experiments, it took decades for the
generality anct significance of McClintock's discovery of trans-
position to be appreciated. McClintock's extraordinary sci-
entific talent and the importance of her early cytogenetic
work were quickly recognized. She became a member of
the National Academy of Sciences in 1944 at the young age
of forty-two, only the third! woman ever to have been elected.
But her subsequent work on transposition led to a periocl
of intellectual aclumbration. While no one doubted her repu-
tation for impeccable experimentation, the concept that
genes count move was so at variance with the regularities of
genetic transmission that permit the construction of ge-
netic maps that its generality was doubted. But in the late
1960s evidence began to accumulate that bacteriophages
and bacteria contain mobile DNA sequences. During the
following two clecacles, it became clear that transposable
elements are not only ubiquitous but are extraordinarily
abundant in the genomes of many organisms. As awareness
of the importance of her discovery grew, so clid public rec-
ognition. Commencing with the National Mecial of Science
in 1970, McCTintock received a number of prestigious awards,
culminating in the award of an unshared Nobel Prize in
Physiology or Medicine in 1983 for her discovery of trans-
position almost forty years earlier.
EARLY LIFE AND EDUCATION
Barbara McClintock was born in Hartford, Connecticut,
to Sara Hancly McClintock and Thomas Henry McCTintock.
Her mother was an accomplished pianist as well as a poet
and painter, and her father was a physician. Barbara was
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214
BIOGRAPHICAL MEMOIRS
the thirc! of four children born while Dr. McCTintock was
struggling to establish his medical practice. By her own ac-
count, McClintock was an ocic! chiTcl and her relationship
with her mother was difficult from the beginning. From
about the age of three until she began school, Barbara lived
in Massachusetts with an aunt and uncle. She accompanied
her uncle, who was a fish dealer, first in a horse-cirawn cart
en c! later in his first motor truck. She reported enjoying
this time and attributed her later interest in cars to watch-
ing her uncle struggle with his vehicle's frequent malfunc-
t~ons.
McCTintock returned home to attend school, and in 1908
the family moved to Brooklyn, New York. McCTintock cle-
scribec3 herself as self-containec! from a very early age, re-
counting her mother's report that she couIct entertain her-
self for unusually Tong periods even in infancy. Later, she
preferred sports, as well as solitary occupations such as read-
ing or just sitting still and thinking. Both parents were quite
unconventional in their attitudes towarc! chiTc! rearing: they
were interested in what the children wouIct and could be,
rather than what they should be. They believer! that formal
schooling was only a part of a child's education, of equal
importance with other experiences. When, for example,
Barbara showed an interest in ice skating, her parents bought
her the best equipment available ant! let her skip school to
skate when the weather was right for it.
Barbara had a very special relationship with her father,
who was extremely perceptive of and responsive to her as a
human being. Even as a child, McCTintock had an uncanny
sensitivity toward people. She recounted having a teacher
who disturber] her intensely because of her perception that
the teacher was spiritually repulsive. Rather than make light
of her reaction to the teacher, McClintock's father took her
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BARBARA McCLINTOCK
215
out of school and providecl her with a private tutor. And
despite the strained relationship between them, McCTintock's
mother fully supported her claughter's unconventional life
style. Barbara clescribed an incident from childhood in which
a neighbor chilled her for playing boys' games in the street,
telling her it was time for her to learn to do the things that
girls do. Upon hearing of the incident, Barbara's mother
telephoned the neighbor and firmly toicl her never again to
speak to her daughter in that fashion.
McClintock attended Erasmus Hall High School in Brook-
lyn, and during her high school years it became increas-
ingly obvious that she wouIc] not outgrow her childhood!
odclities and become a conventional young woman. She clis-
coverect science; she lovecl to learn, and most of all, to
figure things out. Barbara recalled her mother's creep con-
cern that she might become a female college professor,
whom her mother viewed as creatures that really didn't be-
Tong to society and had a difficult life. During this period,
Barbara too became increasingly aware that cloing what she
wanted to do would have painful consequences. But she
knew, as well, that she had to follow her own inclinations
whatever the consequences.
At the time McClintock graduated from high school in
HIS, the family situation was difficult. Although Barbara
had set her heart on attending Cornell University, there
was very little money and her mother was firmly opposed to
further education for her daughters, believing that it macle
them unmarriageable. Barbara took a job at an employ-
ment agency and spent evenings continuing her education
by reacling in the library. Just clays before the semester started
and with the intervention of her father, the decision was
reversed. Barbara took a train to Ithaca and began her studies
at Cornell, where she wouicl stay to earn her doctor of
philosophy degree.
. · . .. .
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BIOGRAPHICAL MEMOIRS
PROFESSIONAL HISTORY
McClintock flourished at Cornell, both socially en c! intel-
lectually. She lovecI learning and she was well likes! so much
so that she was elected president of the women's freshmen
class. But the decisions she macle cluring her university years
were consistent with her adamant indivicluaTity and self-con-
tainment. She enjoyoct her social life, but she knew that
none of her relationships wouIc3 last. Her comfort with soli-
tude ant! the tremendous joy that she experienced in know-
ing, learning, and understanding were to be the defining
themes of her life. In her junior year, after a particularly
exciting course in genetics, her professor invited her
to take a graduate course in genetics. After that, she was
treated much like a graduate student, en c! by the time she
hac! f~nishec! her undergracluate coursework, there was no
question in her mincI: she hac! to continue her studies of
genetics.
But while Cornell had a group of outstanding geneticists,
genetics was taught in the plant breeding department, which
clicl not take female graduate students. So McClintock regis-
terec! in the botany department with a major in cytology
ant! a minor in genetics and zoology. She began to work as
a pair! assistant to Lowell Randolph, a cytologist who had
been appointee! to a position at Cornell supported by the
U.S. Department of Agriculture to complement the work of
the maize geneticists anti, it was hoped, strengthen the maize
plant breeding efforts. McCTintock ant! Randolph ctid not
get along well ant! soon dissolved their working relation-
ship, but as her colleague en c! lifelong friend Marcus Rhoacles
later wrote: "Their brief association was momentous because
it lee! to the birth of maize cytogenetics." The initial task of
reliably identifying each of the ten maize chromosomes hac!
not yet been accomplished. Progress was limited by the in-
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BARBARA McCLINTOCK
217
acloquacy of the existing staining techniques, as well as the
fact that the chromosomes in the root tip material gener-
ally used for such studies could not be reliably clistinguishecI.
McClintock solved both problems. As Rhoacles relater! it:
It was McClintock who capitalized on the use of Belling's new acetocarmine
smear technique. In the course of her triploid studies, she had discovered
that the metaphase or late prophase chromosomes in the first microspore
mitosis were far better for cytological discrimination than were root tip
chromosomes in paraffin sections. In a few weeks' time she had prepared
an idiogram of the maize chromosomes, which she published in Science.
This was McClintock's first major contribution to maize
genetics and laicl the groundwork for a veritable explosion
of discoveries that connecter! the behavior of chromosomes
with the genetic properties of the organism, cleaning the
new f~elct of cytogenetics. McClintock was awardecl the cloc-
tor of philosophy degree in 1927 en c! appointee! an instruc-
tor. She had no thought of leaving Cornell en c! she knew
exactly what needled to be clone next: the maize genetic
linkage groups hacl to be assigned to chromosomes. Again
in Rhoacles's words: "The years at Cornell from 1928 to
1935 were ones of intense cytogenetical activity. Progress
was rapid, the air electric." The group was small, including
Professor R. A. Emerson, the founder of maize genetics,
McClintock, Beadle, Burnham, Rhoades, en c! Randolph, to-
gether with a few graduate students. McClintock had by
then cliscoverecl that the pachytene chromosomes in mi-
crosporocytes were far superior to those of microspores for
cytogenetic work, and the discoveries followed each other
in rapid succession. Each linkage group was soon assigned
to a chromosome, and the physical correlates of their ge-
netic behavior became the primary focus of investigation.
A new graduate student, Harriet Creighton, joined the
group in 1929. McCTintock took charge of organizing her
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218
BIOGRAPHICAL MEMOIRS
program of graduate study, persuading her to major in cy-
tology and genetics. In the spring of the following year,
McClintock suggested that Creighton take on the work of
establishing a correlation between genetic recombination
and the chromosomal crossovers that could be observed
cytologically. McClintock provided stocks that had the ap-
propriate genetic and cytological markers and guided the
work, which shower] for the first time that the genetic re-
combination was a reflection of the physical exchange of
chromosome segments. The work, authored by Creighton
and McClintock, was published in the Proceedings of the Na-
tional Academy of Sciences in 1931 and was perhaps
McClintock's first seminal contribution to the science of
genetics, many more of which were to follow. Among the
most important of her discoveries during the next few years,
sometimes made alone, sometimes together with others, were
that sister chromatics also exhibit genetic and cytological
crossing-over, that genes can be physically localized on the
chromosomes, that nonhomologous chromosome pairing
has genetic consequences, that the formation of ring-shaped
chromosomes accounts for certain types of phenotypic var-
iegation, that the centromere is divisible, that broken chro-
mosomes can undergo repeated cycles of fusion and break-
age, and that a particular chromosomal site, the nucleolus
organizer region (NOR), is essential to the development of
the nucleolus.
Although McClintock's fame was growing, she had no
permanent position. Cornell was hospitable to women stu-
dents, but it had no women professors in fields other than
home economics. Between 1931 and 1933, McClintock was
supported by a fellowship from the National Research Council
and worked at the California Institute of Technology and
the University of Missouri, as well as Cornell. Lewis Stadler
invited her to examine the chromosomes of X-irradiated
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BARBARA McCLINTOCK
219
plants that showed various abnormalities. She found that
the irradiation had caused a variety of structural changes in
the chromosomes, including transIocation, inversions, dele-
tions, and the formation of ring chromosomes. Coming to
Cal Tech at T. H. Morgan's invitation, McClintock began to
study the point at which the nucleolus attached to the chro-
mosome. This lee! to her identification of the NOR
(McCTintock rued the grammatical error she macle initially
in naming this site the "nucleolar organizing bo(ly") en c! a
description of its properties. She user! stocks in which a
transiocation had broken the NOR into two segments, and
her main conclusion was that each part of the NOR couIct
organize an inclependent nucleolus and thus the NOR was
genetically subdivisible. Describing the effect of McClintock's
NOR publication, cell biologist Joseph Gall has written:
Out of the hundreds of papers we have each read, a half dozen or so stick
in our minds because of their beautiful logic, their clarification of an oth-
erwise obscure set of data, or simply their technical elegance.... For me,
one of Barbara McClintock's early cytogenetic papers falls in this category-
her analysis of the nucleolus of maize published in 1934 in the Zeitschr~ft
fur Zellforschung and Mikroskopische Anatomie under the title, "The relation
of a particular chromosomal element to the development of the nucleoli in
Zea ways."
In 1933 McCTintock received a Guggenheim Fellowship
to go to Germany. McClintock was utterly unprepared for
what she encountered in prewar Germany, and she returnee!
to Cornell before the year hacl elapsecI. Her prospects were
clismal. She hacl completer! graduate school seven years ear-
lier and had aIrea(ly attained international recognition, but
as a woman she had little hope of securing a permanent
academic position at a major research university. Emerson
obtained a grant from the Rockefeller Foundation to sup-
port her work for two years. Nominally pair! as Emerson's
assistant, she continued to work inclepen~lently. McCTintock
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BIOGRAPHICAL MEMOIRS
was cliscouraged and resentful of the disparity between her
prospects and those of her mate counterparts. Her extraor-
ctinary talents and accomplishments were wiclely appreci-
atect, but she was also seen as "difficult" by many of her
colleagues, in large part because of her quick minct and
intolerance of second-rate work and thinking. And while a
number of prominent colleagues sought to help secure her
an appropriate academic position, the fact remained that
few positions commensurate with her accomplishments were
open to women.
Finally, in 1936 Lewis Stadler was able to convince the
University of Missouri to offer her an assistant professor-
ship. She accepted the position en c! began to follow the
behavior of maize chromosomes that tract been broken by
X-irracliation. She learner! that the ends of newly broken
chromosomes tend to fuse with each other, creating dicen-
tric chromosomes that break again when a cell divicles and
chromosomes are distributed to the daughter cells. She also
clescribec! conditions uncler which broken chromosomes
"healed" or were repaired in some way so that they could
function normally. She reported briefly in a paper pub-
lished in Genetics in 1944 that in a certain stock a broken
chromosome end that wouic! normally "heal" during clevel-
opment of the embryo failed to do so. This implied that
the addition of chromosome ends, termec! telomeres, was
an active genetic process ant! that the responsible gene in
the stock hacI been inactivated by mutation. Elizabeth
Blackburn, who discoverer! the enzyme that acicis telomeres
to chromosomes, wrote that "this information was in my
mincl when T macle the decision to look for an enzymatic
activity that adds telomeric DNA to DNA antis."
Though McClintock's reputation continued to grow (she
was elected! vice-presiclent of the Genetics Society in 1939),
her position at Missouri remained tenuous. She unclerstoocI
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BARBARA McCLINTOCK
221
soon after her arrival that hers was a special appointment.
She found herself excluclecl from regular academic activi-
ties, inclu(ling faculty meetings, and eventually came to the
realization that she was not only unlikely to be promoted
but that her continued employment clependect on StacIler's
presence. In 1941 she took a leave of absence from Mis-
souri and clepartec] with no intention of returning. She wrote
her friend Marcus Rhoades, who had just taken a position
at Columbia University, asking where he was going to grow
his corn. He was planning to go to CoIc! Spring Harbor for
the summer. An invitation for McCTintock was arranged
through MilisTav Demerec, who was a member of the Ge-
netics Department of the Carnegie Institution of Washing-
ton, then the dominant research laboratory at CoIc3 Spring
Harbor. Demerec became the clepartment's director late
that year and offered McClintock a year's research appoint-
ment. Though hesitant to commit herself, McClintock ac-
cepted. When Demerec proposed making the appointment
permanent, McClintock was quite reluctant but agreed to
fly to Washington to speak with Vannevar Bush, then presi-
clent of the Carnegie Institution. McCTintock recalled that
they took to each other immecliately ant! that both enjoyed
the visit immensely. Bush supported Demerec's wish to ap-
point McCTintock as a permanent member of the research
staff. McClintock accepted, still unsure whether she wouIct
stay.
McClintock clid stay. She was a staff member of the Carnegie
Institution of Washington's Genetics Department until ~ 967,
whereupon she became distinguished service member of
the Carnegie Institution, remaining at CoIcl Spring Harbor
until her death in 1992. Carnegie gave her the freedom to
do her work unfettered by teaching and other academic
duties. McClintock's clisTike of making commitments was a
given: she always wanted to be free free to clo exactly what
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BIOGRAPHICAL MEMOIRS
it must be so! " Such was the intellectual respect that
McClintock commanded—anti such was the strangeness of
concept and complexity of her experimentation.
McCTintock was deeply frustrated by her failure to com-
municate, but her fascination with the unfoicting story of
transposition was sufficient to keep her working at the highest
level of physical ant! mental intensity she couIc! sustain.
Her work on transposition was interrupted only twice. The
first interruption was a visit to Stanford in 1944 in response
to an invitation from George BeacIle, who thought she was
precisely the person to work out the problem of identifying
the chromosomes of the moist Neurospora, which hacl be-
come.a popular organism for molecular geneticists. The
second occurred in the late 1950s when the National Acac3-
emy of Sciences established a committee to identify and
collect indigenous races of maize in Central and South
America out of concern that the introduction of high-yielc3-
ing agricultural hybrids wouicl result in their disappearance.
McClintock was asked to help train local cytologists to carry
out the work of classifying the maize races by chromosome
morphology. McClintock spent the winters of 1958 and 1960
in Central and South America, fascinated by the emerging
realization that the spread of maize through the region
couIcI be tracker! by the chromosome constitution of the
indigenous populations. The work was summarized briefly
in the Yearbooks of the Carnegie Institution, appearing as a
full monograph in 1978.
But transposition remained McCTintock's central passion.
By the time of her formal retirement, she tract accumulated
a rich store of knowlecige about the genetic behavior of two
markedly different transposable element families. She was
sufficiently confident of the importance of her work to care-
fully preserve all of the stocks with mutant elements that
she accumulatecl along the way, perhaps in unconscious prepa-
OCR for page 227
BARBARA McCLINTOCK
227
ration for the new generation of molecular geneticists. And
incleecI, beginning at about the time her active fieldwork
enclect, transposable genetic elements began to surface in
one experimental organism after another. These cliscover-
ies began in an altogether different age. In the two clecacles
between McCTintock's original genetic discovery of transpo-
sition and its rediscovery, genetics hacl undergone as pro-
found a change as the cytogenetic revolution that hacI oc-
currec3 in the second and thirc! decacles of the century. The
genetic material had been identifies] as DNA, the manner
in which information was encocled in the genes hacI been
deciphered, and methods hac3 been clevisect to isolate ant!
study indiviclual genes. Genes were no longer abstract enti-
ties known only by the consequences of their alteration or
loss: they were real bits of nucleic acid] that could be iso-
lated, visualized, subtly altered, en c! reintrocluced into liv-
· .
ng organisms.
Thus, soon after the initial realization that mutations of
a certain type that occurred in bacterial viruses might be
attributable to the insertion of a foreign DNA sequence,
visual evidence was obtained by electron microscopic analy-
sis of heteroduplexes between homologous DNA sequences
having and lacking the insertion. The newly inserted mo-
bile elements appeared as unpaired loops of DNA extencl-
ing from the DNA cluplex. Mobile genetic elements were
no longer abstract concepts. Although the study of maize
transposable elements had been an active and productive
fielcl of research since Emerson's original studies on varie-
gation at the P locus long before McClintock explicates! the
underlying genetic mechanisms, the recognition that mo-
bile elements are ubiquitous and in fact extraorclinarily abun-
dant components of the genomes of many, if not all, organ-
isms grew slowly cluring the 1970s and 1980s.
My first encounter with McClintock, which was to lead
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BIOGRAPHICAL MEMOIRS
eventually to the molecular cloning and characterization of
the maize elements, took place during a visit to the CoIcI
Spring Harbor Laboratory in 1978. The laboratory itself
was no longer the same institution that McClintock had
joined almost four decades earlier. The Genetics Depart-
ment had been closed by the Carnegie Institution of Wash-
ington, although a Genetics Unit consisting of McCTintock
and A. Hershey, both retired, hac] been maintained. i. D.
Watson was by then the director of a vastly larger complex
of laboratories at Coicl Spring Harbor, all engages] in mo-
lecular biological investigations. T had been asked to give a
seminar at the CoIct Spring Harbor Laboratory on my
postdoctoral work in Don Brown's laboratory at the Carnegie
Institution of Washington's Department of Embryology in
Baltimore. Although McClintock was unable to attend the
lecture, T encounterer! her by chance in a hallway of the
Demerec Laboratory, en c! she invites! me to her spacious
laboratory for a chat. We talked for several hours, ant! ~ was
drawn to the clarity en c! depth of her discourse, no matter
the subject. It was so at variance with her reputation for
obscurity that ~ was prompted to react her papers from be-
ginning to end upon my return to Baltimore. T was intrigued
with what ]: fount! to be a marvelous genetic detective story,
and when ~ received an unexpected offer of a permanent
staff position at Carnegie's Embryology Department, T im-
mecliately decided to tackle the molecular analysis of the
maize elements.
The task ~ had taken on proved daunting, as much be-
cause of the distance between McClintock's classical genetic
approach en cl that of the molecular biologist as because
plant molecular biology simply clidn't exist yet. Our rela-
tionship began in earnest when ~ grew my first corn crop
consisting of McCTintock's transposable element stocks dur-
ing the summer of 1979 at the Brookhaven National Labo-
OCR for page 229
BARBARA McCLINTOCK
229
ratory, where we were kindly offered space and help by Ben
and Frances Burr. Although McClintock was highly critical
of mY first efforts at maize genetics, enough of the right
crosses got done despite my ignorance, so that ~ had the
material ~ needed to begin the molecular cloning of first
the Ac and Ds elements and, later, the sum element. Our
first interactions were difficult, and it took several years
before we were comfortable with each other's way of think-
ing. But in time we both came to value deeply the intellec-
tual as well as the personal side of our relationship.
By the time the maize elements were cloned and their
molecular analysis began, the importance of McClintock's
discovery of transposition was widely recognized. She re-
ceived the Kimber Genetics Award in 1967, the National
Medal of Science in 1970, and the Lewis S. Rosensteil Award
and the Louis and Bert Freedman Foundation Award in
1978. In 1981 she was named prize fellow laureate of the
MacArthur Foundation and received the Wolf Prize and the
Lasker Basic Medical Research Award. In 1982 she shared
the Horwitz Prize. Finally, in 1983, thirty-five years after
publication of the first evidence for transposition, McClintock
was awarded the Nobel Prize for Physiology or Medicine.
Yet while the money attached to these prizes increased her
financial security, something to which she'd given little
thought in earlier years, she found the ceremonies arduous
and the attendant publicity and adulation utterly repug-
nant. She longed for her privacy, and she was exhausted
and disturbed by the endless stream of requests that only
seemed to grow in volume with each award. Suddenly ev-
eryone wanted her: there were honorary degrees, keynote
speeches, lectures, interviews even autograph hunters.
And still, through it all, McClintock never lost her con-
nection with science- she never retired. She continued to
live at Cold Spring Harbor, spending her last years in a
OCR for page 230
230
BIOGRAPHICAL MEMOIRS
spartan apartment on the ground floor of Hooper House, a
women's (lormitory heavily used during the summer meet-
ings season at the laboratory. She attencled every session of
the annual Cold Spring Harbor Symposium, as well as semi-
nars, the year around. She react voraciously, lamenting her
failing vision. Her laboratory was fillet! with books on all
subjects, and the tables were coverer} with stacks of articles
copied from current journals, many with sentences care-
fully underlinecl here and there, giving evidence of careful
attention. She was keenly aware of every clevelopment in
the molecular and genetic analysis of the maize transpos-
able elements as it unfoIclec3 in my laboratory and else-
where. She took special interest in the analysis of the com-
plex ant! elegant Spm family of elements, my own particular
favorite. Not until the last few years of her life diet the
molecular en c! genetic studies on this family of elements
become so complex that she began to Once it cliff~cult to
follow and remember the details. Even when ~ visited CoIcI
Spring Harbor in 1991 to give a course lecture on the mo-
lecular genetics of the maize transposable elements,
McClintock sat through the entire session, which lasted late
into the evening. Her questions were penetrating en c! her
observations invariably wicienecI the discussion: the students
were amazed.
It was during this visit that I was approached by Jim Inglis
of the CoIcl Spring Harbor Press to assemble a volume in
honor of McClintock's ninetieth birthday the following year.
T took on the project, despite qualms that Barbara wouIc3
find this not a gift but another burden. David Botstein, who
joined me in this effort, anct ~ approached a number of
individuals whose lives hac! intersected with McClintock's
to write for this volume. What emerges! was The Dynamic
Genome, a collection of varied essays each reflecting the pur-
suits and passions ignited by the sparks ant! embers scat-
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BARBARA McCLINTOCK
23
terecl from the fierce blaze of McClintock's intellect through
the clecacles of this century of genetics. Many of the au-
thors joiner! in the celebration of her ninetieth birthday at
the home of Jim Watson, not far from her moclest apart-
ment on the laboratory grour~cis. She knew nothing of the
book but recognized her friends even Harriet Creighton,
her first "unofficial" graduate student, had macle the trek
to Coicl Spring Harbor. We settlecl Barbara on Jim's front
porch and T began to react aloud the introduction and the
list of authors and their essays. At first she joker! a bit,
ctiscomf~tec! by the attention. But soon her face began to
glow as she perceives! the depth of unclerstanding and re-
spect gathered arounc! her, lovingly collectecl between the
covers of the book. She said later it was the best party ever
for her, though she acimitted that it had taken a week to
recover at her age. She was sure that she would die at ninety
and a few months later she was gone, drifting away from
life gently, as a leaf separates from an autumn tree. What
Barbara McClintock was and what she left behind are elo-
quently expressed in a few short lines written many years
earlier by her friend and champion Marcus Rhoades, whose
cleath precedes! hers by a few short months:
One of the remarkable things about Barbara McClintock's surpassingly beautiful
investigations is that they came solely from her own labors. Without techni-
cal help of any kind she has by virtue of her boundless energy, her com-
plete devotion to science, her originality and ingenuity, and her.quick and
high intelligence made a series of significant discoveries unparalleled in
the history of cytogenetics. A skilled experimentalist, a master at interpret-
ing cytological detail, a brilliant theoretician, she has had an illuminating
and pervasive role in the development of cytology and genetics.
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232
BIOGRAPHICAL MEMOIRS
THE QUOTATIONS ATTRIBUTED to McClintock are from her publica-
tions on transposition, primarily the annual reports appearing in
the Yearbooks of the Carnegie Institution of Washington; all of these
are reproduced in The Discovery and Characterization of Transposable
Elements: The Collected Papers of Barbara McClintock (New York: Gar-
land Publishing, 1987~. All other quotations, with the exception of
the first and last (Bateson and Rhoades), appear in the chapters by
the individuals to whom they are attributed in The Dynamic Genome:
Barbara McClintock's Ideas in the Century of Genetics (ea. N. Fedoroff
and D. Botstein; Cold Spring Harbor: Cold Spring Harbor Press,
1992~. The Bateson quotation appears in E. A. Carlson's, The Gene:
A Critical History (Philadelphia: W. B. Saunders). The final quota-
tion of M. M. Rhoades was taken from an undated document in the
files of the Carnegie Institution of Washington titled "Barbara
McClintock: Statement of Achievements," possibly prepared in sup-
port of her nomination for an award. Other than my own recollec-
tions of conversations with McClintock, my principal source of in-
formation about her early life and the chronology of later events
was E. F. Keller's, A Feeling for the Organism: The Life and Work of
Barbara McClintock (San Francisco: Freeman, 1983), as well as a copy
of McClintock's curriculum vitae, given by her to me in about 1980
together with one of her two complete collections of her reprints.
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BARBARA McCLINTOCK
SELECTED BIBLIOGRAPHY
1929
Chromosome morphology in Zea mays. Science 69:629.
1930
233
A cytological demonstration of the location of an interchange be-
tween two nonhomologous chromosomes of Zea mays. Proc. Natl.
Acad. Sci. U.S.A. 16:791-96.
1931
With H. E. Hill. The cytological identification of the chromosome
associated with the R-G linkage group in Zea mays. Genetics 16:175-
90.
The order of the genes C, Sh, and Wx in Zea mays with reference to
a cytologically known point in the chromosome. Proc. Natl. Acad.
Sci. U.S.A. 17:485-91.
With H. B. Creighton. A correlation of cytological and genetical
crossing-over in Zea mays. Proc. Natl. Acad. Sci. U.S.A. 17:492-97.
1932
A correlation of ring-shaped chromosomes with variegation in Zea
mays. Proc. Natl. Acad. Sci. U.S.A. 18:677-81.
1933
The association of non-homologous parts of chromosomes in the
mid-prophase of meiosis in Zea mays. Z. Zellforsch. Mibrosk. Anal.
19:191-237.
1934
The relation of a particular chromosomal element to the develop-
ment of the nucleoli in Zea mays. Z. Zellforsch. Mibrosk. Anat. 21:294-
328.
1939
The behavior in successive nuclear divisions of a chromosome bro-
ken at meiosis. Proc. Natl. Acad. Sci. U.S.A. 25:405-16.
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234
BIOGRAPHICAL MEMOIRS
1941
The stability of broken ends of chromosomes in Zea mays. Genetics
26:234-82.
1942
The relation of homozygous deficiencies to mutations and allelic
series in maize. Genetics 29: 478-502.
The fusion of broken ends of chromosomes following nuclear fu-
sion. Proc. Natl. Acad. Sci. U.S.A. 11:458-63.
1945
Neurospora: I. Preliminary observations of the chromosomes of Neu-
rospora crassa. Am. f. Bot. 32:671-78.
1948
Mutable loci in maize. Carnegie Inst. Washington Yearb. 47: 155-69.
1950
The origin and behavior of mutable loci in maize. Proc. Natl. Acad.
Sci. U.S.A. 36:344-55.
1951
Chromosome organization and genie expression. Cold Spring Harbor
Symp. Quant. Biol. 16:13-47.
1953
Induction of instability at selected loci in maize. Genetics 38:579-99.
1956
Intranuclear systems controlling gene action and mutation. Brookhaven
Symp. Biol. 8:58-74.
Controlling elements and the gene. Cold Spring Harbor Symp. Quant.
Biol. 21:197-216.
1961
Some parallels between gene control systems in maize and in bacte-
ria. Am. Nat. 95:265-77.
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BARBARA McCLINTOCK
1965
235
The control of gene action in maize. BrooLhaven Symp. Biol. 18:162-
84.
1968
Genetic systems regulating gene expression during development.
Dev. Biol. Suppl. 1:84-112.
1971
The contribution of one component of a control system to versatil-
ity of gene expression. Carnegie Inst. Washington Yearb. 70:5-17.
1978
Development of the maize endosperm as revealed by clones. In The
Clonal Basis of Heredity, ed. S. Subtelny and I. M. Sussex, pp. 217-
37. New York: Academic Press.
Mechanisms that rapidly reorganize the genome. Stadler Symp. 10:25-
47.
Significance of chromosome constitutions in tracing the origin and
migration of races of maize in the Americas. In International Maize
Symposium, ed. W. D. Walden, pp. 159-84. New York: Wiley.
1984
The significance of responses of the genome to challenge. Nobel
lecture. Science 226:792-801.
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Representative terms from entire chapter:
spring harbor
