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TRACY MORTON SONNEBORN
October I 9. I 905-fanuary 26, I 98 '
BY JOHN R. FREER, JR.
WITH PIPETTES, CULTURE VESSELS, a low- and a high-power
microscope, en c! a few collections of water from nearby
poncis en c! streams, Tracy Sonneborn worker! with species
of the Paramecium aurelia group en c! learner! more about
the basic biology of protozoa than anyone else ever has. He
cliscoverec! mating types in Paramecium, thereby advancing
biological studies on the protozoa by a quantum leap. He
clemonstratec! simple Menclelism en c! establisher! the be-
havior of genes, nuclei, en c! cytoplasm in the complex pro-
cesses of the life cycle. He shower! that the uniparental
nuclear reorganization that occurs perioclically in many para-
mecia is the sexual process of autogamy, not the asexual
process of endomixis as originally thought.
He cliscoverec! macronuclear regeneration en c! cytoplas-
mic exchange, both invaluable for genetic analysis. He clem-
onstratec! caryonicial inheritance, showing that incliviclual
ciliate macronuclei, although descended asexually from iden-
tical micronuclei, can acquire different genetic properties
during their development. He showed that the phenotype
of Paramecium is cleterminec! by the macronucleus, not the
micronucleus. He acivancec! our unclerstancling of the states
of immaturity, maturity, and senescence in the life cycle of
the ciliatec! protozoa, showing that aging can be reverser!
269
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B I O G RA P H I C A L
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by autogamy as well as conjugation. His analysis of species
in lower organisms proclucec! novel evolutionary concepts.
Primarily he will be rememberer! for his studies on non-
Menclelian inheritance. When he began his work, the role
of the cytoplasm in heredity was entirely unknown. He shower!
that the various cases of non-Menclelian inheritance conic!
be ciassifiec! into distinct groups, most involving interac-
tions between nuclear genes en c! the cytoplasm. His early
studies on the cytoplasmic factor "kappa" established the
first case of cytoplasmic inheritance in animals, en c! subse-
quent work by him en c! his students shower! that intracellu-
lar symbioses en c! cell organelles have become inextricably
combiner! cluring evolution. His studies on surface proteins
shower! that complex systems of interacting elements in pro-
tein synthesis can create stable states of gene expression
clepenclent on factors present in the cytoplasm. In a most
elegant series of experiments on the ciliate cortex, he en c!
his collaborators shower! that the form en c! arrangement of
preexisting structures determine the form en c! arrangement
of new structures.
Finally, studying mating type en c! an unusual trichocyst
mutant, he uncoverec! the first examples of a strange non-
Menclelian phenomenon in which the macronucleus of cili-
ated protozoa determines the cytoplasm, and the cytoplasm
in turn determines newly forming macronuclei, thereby pass-
ing genetic information from the old disintegrating macro-
nucleus to the newly forming macronuclei.
PERSONAL HISTORY
i
Tracy Morton Sonneborn was born on October 19, 1905'
n Baltimore, MarylancI. His mother was Daisy Bamberger,
en c! his father, Lee, was a businessman. Both encourages!
him in his education. Others having an important influ
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TRACY MORTON SONNEBORN
271
once in his early life were his uncle, Jacob Bamberger, en c!
his cousin, Louis Bamberger. It was Louis Bamberger who
establishec! the Institute for Advance c! Stucly at Princeton.
As a teenager, Tracy became interested in the humanities
en c! religion en c! at one point seriously consiclerec! becom-
ing a rabbi. However, his beliefs soon changed, and, after
attending Baltimore Polytechnic High School for two years
en c! Baltimore City College High School for two more years,
he enterer! Johns Hopkins University with the intention of
studying literature. His interests changer! to science when
he took an introductory course in biology taught by E. A.
Ancirews. He receiver! the B.A. degree from Hopkins in
1925.
He then began graduate work on the flatworm, Stenostomum,
uncler the supervision of Herbert S. Jennings, director of
the Zoological Laboratories at Johns Hopkins. Jennings was
a remarkable scholar, one of the pioneers of biology. He
publisher! extensively en c! was renownec! as a scientist, phi-
Tosopher, en c! educator. Jennings hac! a broac! view of biol-
ogy. He worker! on lower organisms en c! was concernec!
with the most funciamental aspects of behavior, inheritance,
development, population biology, and evolution. Jennings
hac! a profounc! influence on Tracy's clevelopment as a sci-
entist. Tracy's passion for thoroughness en c! cletail en c! his
. . .
broac! view of biology were like that of his teacher. He re-
ceivec! the Ph.D at Johns Hopkins in ~ 928.
At that time, he receiver! a National Research Council
fellowship and spent 1928 and 1929 with Jennings at Hopkins
working on the ciliate, Colpidium. In 1929 he marries! Ruth
Meyers, it was a happy union that lasted until his death
fifty-two years later. At the enc! of Tracy's fellowship in 1930
his attempts to obtain a faculty position failecI, but he was
offerer! a position as a research assistant at Hopkins with
Jennings, who hac! just obtainer! a research grant from the
i,
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B I O G RA P H I C A L
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Rockefeller Foundation for work on Paramecium. During the
perioc! 1930 to 1939, Tracy hell! the positions of research
associate en c! then associate at Johns Hopkins. After seven
years of basic studies on the life cycle of Paramecium, he
made his discovery of mating types in 1937, which immedi-
ately won him fame as an investigator. In 1939 Fernanclus
Payne persuaclec! him to accept a position at Indiana Uni-
versity as an associate professor. There he stayer! for the
rest of his life, becoming professor in 1943, clistinguishec!
service professor in 1953, en c! clistinguishec! professor emeri-
tus in 1976.
His first son, Lee, was born in 1929 in Baltimore en c!
became a mathematician. His seconc! son, David, was born
in 1934, also in Baltimore and, like his father, became a
biologist. Tracy's family life was remarkable. His wife, Ruth,
was eclucatec! as a social worker en c! might have hac! a clis-
tinguishec! career of her own. Instead, she clevotec! her life
to family en c! to his career. He was cleeply grateful to Ruth,
for she macle it possible for him to devote himself virtually
full time to his scholarly activities. She was clearly the mother
en c! personal confidant of all the many students en c! post-
doctorals who passed through the Sonneborn Laboratory
at Indiana University. When Tracy arriver! home from work,
his role of eminent scientist whose every wore! was carefully
consiclerec! by his students changer! completely. He was just
one more member, albeit a greatly belovec! member, of a
very close, well-acljustecI, happy family. At one point cluring
Thanksgiving clinner at my first visit to his home, emit! all
the Slav conversation.
Tracy was finally able to get in an
O , ,
opinion on the topic at hancI. There follower! a suciclen
silence arounc! the table follower! by a pronouncement from
his youngest son, age five: "OIc! crummy Dacicly." As a new
graduate student I was incleec! shockocI, for at the labora-
tory his every pronouncement was worthy of the utmost
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TRACY MORTON SONNEBORN
273
respect en c! consideration, but here everyone thought it
was a splenclic! joke. Throughout his life these close rela-
tions within his family never changed.
Tracy was vitally interested in the activities en c! accom-
plishments of those about him. In conversation he spoke
quickly and thought even more quickly. His incisive and
often blunt comments were a bit intimidating at first for
some of his new students, but his kinciness en c! humor macle
him easy to engage in conversation. After a full clay in his
office en c! laboratory, he spent almost every evening think-
ing, writing, en c! making notes. For most of his life he met
for a long session once a week in the evening with his stu-
clents en c! others in his research group. Music en c! bircis
were his primary hobbies, but they took only a small por-
tion of his time.
Every task that ciaimec! his attention an experiment, a
new course, a research report, a manuscript to review, a
stuclent's class paper somehow became the most impor-
tant thing in the woric! to him. It hac! to be clone with
thoroughness en c! perfection. Nothing was too much trouble.
An unclergracluate lecture was as important as a keynote
,
aciciress at a major scientific meeting. He regularly took his
place at unclergracluate registration, interviewing each stu-
clent (often 200 or 300), making sure all hac! the appropri-
ate backgrounc! en c! interests for his class. He once com-
mentec! that teaching en c! research in no way interfered
with each other, for all one neecis to clo is devote forty
hours per week to each. For him that was clearly an uncler-
statement.
His lectures, whether for large classes, small classes, un-
clergracluates, graduates, or scientific papers presented to
his peers, were presented in a clear en c! exciting fashion.
His enormous enthusiasm spreac! to all his audience. After
a lecture at Goucher College in 1937 describing his first
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B I O G RA P H I C A L
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fincling of mating types, his audience was really to follow
him out the floor en c! back to his laboratory to fins! what
the experiments in progress wouIc! show. His first course at
Indiana University, which was supposes! to cover all the in-
vertebrates, got no farther than the flatworms. He user! to
joke that when his department chairman, Fernanclus Payne,
learner! that he hac! only coverer! protozoa, coelenterates,
en c! flatworms in his course on invertebrates he almost got
firecI. It is noteworthy that two members of the class went
on to careers studying protozoa, one even shifting from a
commitment in another fielcI. The excitement he gener-
atec! was genuine en c! long lasting. For example, when he
lecturer! on algae in a course with no formal laboratory, it
was routine to see algae appear spontaneously in the vari-
ous laboratories in which the graduate students workocI, as
they attemptec! to repeat en c! carry some of the experi-
ments a step further.
In the late 1940s his laboratory enIargecI. He brought in
Wilhelm van Wagtenclonk, a biochemist from Oregon, who
Sonneborn hoper! wouIc! work out the biochemical basis
for the many genetic traits that he was investigating. How-
ever, it turner! out that these traits were not reacliTy acces-
sible to biochemical investigation. Van Wagtenclonk cleciclec!
that it was necessary first to develop a defined medium for
culturing Paramecium. This endeavor prover! to be very clif-
ficult en c! time consuming. In the enc! he was successful,
but it requires! the remaining portion of Van Wagtenclonk's
research career to achieve success. Early on, Ruth Dippell
became his research technician. Ruth eventually receiver!
the doctorate degree en c! became a faculty member, but
she always worker! closely with him in her research. As the
laboratory enIargec! en c! his Ph.D. students increaser! in
number, numerous postdoctoral workers also came, many
from Europe en c! some from Japan en c! China. Bloomington
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TRACY MORTON SONNEBORN
275
became the Mecca for all who wouic! work on Paramecium.
These investigators went on to important positions in uni-
versities en c! research institutes throughout the worIcI. Soon
most of the work on Paramecium was being clone by those
who hac! passer! through his laboratory.
He continues! to clo research until his cleath in
Bloomington in 1981, following a short illness with cancer.
Tracy receiver! many honors cluring his career. He was
electec! a member of the National Academy of Sciences in
1946, a foreign member of the Royal Society of London in
1964, a member of the American Academy of Arts en c! Sci-
ences in 1946, en c! a member of the American Philosophi-
cal Society in 1952. He receiver! the Kimber Genetics Awarc!
of the National Academy of Sciences in 1939, the Menclel
Centennial Mecial of the Czechoslovakian Academy of Sci-
ences in 1965, en c! the Newcomb-Clevelanc! Mecial en c! Prize
of the American Association for the Advancement of Sci-
ence in 1946. He was an honorary member of the French
Society of Protozoology, the Genetics Society of Japan, en c!
the American Society of Protozoologists. He receiver! hon-
orary cloctor's degrees from Johns Hopkins University, North-
western University, Indiana University, the University of
Geneva (SwitzerIancI), en c! the University of Westphalia (Ger-
many). He server! as president or boars! member of many
scientific organizations en c! gave numerous prestigious lec-
tures in this country en c! abroad.
~. . ..
STENOSTOMUM
PROFESSIONAL HISTORY
When Tracy began his work for the Ph.D. in 1926, his
mentor, Jennings, believer! that, although Menclelian genes
were responsible for most of the traits in higher organisms,
other genetic mechanisms might also exist. These factors
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B I O G RA P H I C A L
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were thought to be especially important in lower organ-
isms, en c! it was also thought that they might be localizes! in
the cytoplasm en c! susceptible to environmental moclifica-
tion. The way to test these speculations was simply to stucly
the effects of environment en c! heredity on the clevelop-
ment of various traits in selectee! lower forms of life. Such
studies were to form the basis of Tracy's whole research
career. His Ph.D. problem was on inheritance in Stenostomum,
which reproduces asexually by clivicling transversely into an
anterior en c! a posterior half. He was able to identify en c!
follow these halves in isolation cultures en c! fount! that pro-
gressive lines of anterior division products were more likely
to age en c! clie than lines of posterior products. He also
exposer! Stenostomum to leas! acetate en c! fount! that abnor-
malities appeared. After such treatments he was able to iso-
late two-heaclec! "monsters" that reproclucec! true to type.
Since these traits were maintainer! for many generations,
they were jucigec! to have a hereditary basis. However, these
variants arose and were lost at a much higher frequency
than one woulc! expect if they were clue to mutations in
simple Menclelian genes.
COLPIDI UM
After his Ph.D. work, Tracy stayed for eleven more years
in Jennings's laboratory at Johns Hopkins. His first work
was on the small ciliate, Colpidium, an organism he hac!
user! to few! his Stenostomum. He cultures! Colpidium on a
strain of bacteria on which they flourished. When he changer!
the bacterium to another less favorable kind, abnormalities
appearec! in the belly form. From these abnormal animals
he was able to isolate double animals, en c! these doubles
reproclucec! true to type indefinitely, even when they were
returnee! to culture on the more favorable bacterium. Again,
the effect of the environment in inclucing abnormal ani
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TRACY MORTON SONNEBORN
277
mats of a particular kinc! in high frequency was not what
one would expect on the basis of mutation in Menclelian
genes.
THE LIFE CYCLE OF PARAMECIUM
Sonneborn began his work on Paramecium when the prob-
lems of genetics, clevelopment, cell biology, en c! evolution
were being attacker! energetically by such workers as Mor-
gan, Sturtevant, Bridges, Darlington, Halciane, Wright,
Demerec, Jennings, Ephrussi, BeacIle, Tatum, Emerson,
McCTintock, en c! StacIler. Sonneborn assumer! his position
as one of that group. His plan for research was simple:
learn all he conic! about a single organism en c! apply his
knowledge generally where applicable. By choosing a single
organism, Paramecium, he thought he conic! attain a mas-
tery of that organism that wouIc! enable him to carry out
sophisticates! experiments impossible for scientists who pick
a single problem en c! move from organism to organism. He
stuck to his plan faithfully, studying Paramecium almost ex-
clusively cluring his whole research career. Sonneborn notes!
that, while protozoa are whole organisms, they are also single
cells, en c! he recognizec! a rare chance to stucly inheritance
inclepenclently of the complex multicellular life cycle that
precluclec! investigations of cellular genetics in most organ-
isms. While procaryotes are also unicellular, he felt that
most studies on bacteria were concernec! with populations
of cells, not incliviclual cells.
A test for Menclelism by brawling analysis conic! not be
macle in the case of either Stenostomum or Colpidium be-
cause both lackey! sexual reproduction. By turning to Para-
mecium, which is able to conjugate en c! exchange germinal
nuclei, he thought clefinitive tests of Menclelism wouic! be
possible. The only problem was that mating reactions, while
common in both nature en c! the laboratory, conic! not be
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B I O G RA P H I C A L
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controller! en c! often occurrec! even in clones (i.e., cultures
clerivec! by binary fission from single celIs). So Sonneborn
set about learning to unclerstanc! en c! control mating en c!
the life cycle.
Members of the Paramecium aurelia complex of species
have a vegetative polyploic! macronucleus that clirectly con-
trols the characters of the cell en c! also two germinal micro-
nuclei that perioclically give rise to new macronuclei. Para-
mecium reproduces vegetatively by binary fission. The
macronucleus clivicles amitotically, en c! the micronuclei cli-
vicle by mitosis. At conjugation en c! autogamy, the oIc! ma-
cronucleus breaks into fragments en c! normally is lost clur-
ing subsequent fissions, while the two micronuclei undergo
meiosis. A single haploic! melotic nucleus then clivicles to
give a migratory en c! a stationary haploic! nucleus. The mi-
gratory nucleus from each conjugant fuses with the station-
ary nucleus of its mate, or in the uniparental process of
autogamy the two products simply fuse with each other. In
each cell the cliploic! zygote micronucleus gives rise by mi-
tosis to four micronuclei. Two remain as micronuclei en c!
two clevelop inclepenclently into macronuclei. At the next
fission the two new macronuclei are segregated one to each
daughter cell, while the micronuclei clivicle mitotically en c!
are clistributec! two to each daughter cell, restoring the nor-
mal vegetative state. Sonneborn was able to control auto-
gamy when he fount! that a rapic! fission rate in an excess
of fresh culture medium inhibited autogamy while starva-
tion inclucec! it, proviclec! the animals hac! undergone a suf-
ficient number of fissions since the last conjugation or au-
togamy. Note that following the first fission after autogamy
en c! conjugation each of the two cells has a macronucleus
derived independently from different micronuclei he called
the two lines "caryonicles." He cliscoverec! that mating within
a caryonicle is seen only rarely, while for the strains of Para
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TRACY MORTON SONNEBORN
283
interpretation was eventually acceptec! by Sonneborn en c!
has recently receiver! support from molecular studies.
PLASMAGENESE
Virtually all the traits Sonneborn encounterer! in his early
studies were non-Menclelian, with strong genie en c! strong
cytoplasmic components. At this point the evidence seemec!
to leac! to the conclusion that cytoplasmic inheritance was
an important component in all cases of inheritance in Para-
mecium. Perhaps in higher organisms that same was true,
but it was being masked by the processes occurring in em-
bryological clevelopment. So at this time the plasmagene
theory was born: It was postulated that all genes in all or-
ganisms produce a self-reproclucing entity that persists
through somatic cell divisions but that is lost cluring sexual
reproduction. The theory was given support by a number
of studies clone by others, especially the studies of Spiegelman
on adaptive enzymes in yeast.
As work progressed, however, it became clear that the
interpretation of the ciata as evidence for plasmagenes was
not valicI. Kappa en c! its relatives turner! out to be symbiotic
bacteria, dependent upon special genes for their mainte-
nance. Further work on the expression of genes for surface
proteins seemec! to be best interpreter! as a special inter-
play of competing inhibitors en c! activators of protein syn-
thesis. Mating-type inheritance was more clifficult to evalu-
ate, but Sonneborn was able to show that mating-type
inheritance was ultimately uncler nuclear control, the cyto-
plasm acting only to transmit information from the old
macronucleus to the newly cleveloping macronucleus. There
was, in fact, no evidence for self-reproducing cytoplasmic
genes.
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THE CORTEX
B I O G RA P H I C A L
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Facet! with these new finclings, the notion of plasmagenes
was cliscarclecI, en c! Sonneborn embarkoc! on his investiga-
tions of the structure of the cellular cortex in Paramecium.
Sonneborn always viewoc! his early work on Stenostomum en c!
Colpidium as incomplete, for, although his two-heaclec! mon-
sters in Stenostomum en c! cloublets in Colpidium arose in high
frequency en c! in response to environmental stimuli in a
cleciclecIly non-Menclelian fashion, the organisms were asexual,
en c! decisive brawling tests were not possible. He found,
however, that cloublets conic! easily be inclucec! in Parame-
cium by exposing conjugating cells to antiserum. He now
set about crossing singles with cloubles. The results ruler!
out Menclelian genes. He also ruTec! out both the presence
of determinants in the Quit! cytoplasm en c! macronuclear
inheritance like that observer! for certain mating types. He
was left with the cortical structure itself as the basis for the
inheritance. Moreover, he en c! his collaborators were able
to show that rearrangements in the pattern of the cilia,
trichocysts, parosomal sacs, en c! fibrillar structures that make
up the cortex also can be inheritec! in the same fashion.
Sonneborn said that these instances were based on a new
principle of inheritance that he caller! "cytotaxis," the abil-
ity of preexisting structures to control the formation and
placement of new structures. Cyto taxis has since been stucI-
iec! extensively in the ciliate cortex by many workers.
Again, Sonneborn proclucec! a brilliant series of experi-
ments. They showed without doubt that preexisting struc-
ture controls the way new structures are former! in the cor-
tex of ciliatec! protozoans. This work was hell! to be a major
new phenomenon in genetics and development, applicable
to all organisms. Currently, it appears that these principles
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TRACY MORTON SONNEBORN
285
are incleec! applicable to other organisms en c! organelles,
but its true general significance is yet to be cleterminecI.
SENESCENCE AND THE LIFE CYCLE
It has been known for many years that after conjugation
many ciliates undergo an immature perioc! of many vegeta-
tive generations in which they are unable to mate. Then
after a perioc! of maturity, if mating floes not occur, there is
a perioc! of senescence en c! finally cleath. Jennings pointer!
out that each stage lasts for such a long perioc! that one
must consoler the stages heritable. The basis for the changes
has remainec! unknown, although recent experimental evi-
clence involving microinjection reinforces the view that its
basis lies within the macronucleus. In any case, it is clear
that the mechanism floes not rely on simple Menclelian
genetics. Sonneborn investigates! the matter in relation to
the unisexual process of autogamy in Paramecium. He fount!
that autogamy collie substitute for conjugation in rejuve-
nating senescent lines of paramecia. Another life-cycle change
he notes! was that after autogamy paramecia must undergo
a certain number of fissions, in some cases a large number,
before cells can undergo another autogamy. The basis for
these life-cycle changes is unknown.
THE SPECIES PROBLEM
When Sonneborn discovered mating types, he found twenty-
eight types among different strains. He was able to show
that only mating type I could mate with mating type II, only
III with IV, en c! so on, for a total of fourteen different
mating pairs. He noted that each pair constituted a single
interbreeding group. Since each group shared a common
gene pool, it was clear that they constituted a series of sib-
ling species. From the beginning he realized the taxonomic
problem presenter! by the situation, for mating types can
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B I O G RA P H I C A L
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not be readily ascertained in the field. Even in the labora-
tory the process is time consuming, requiring the isolation
and mixing of clones with standard mating types. He real-
ized the problem that would be presented to taxonomists if
the groups were given binomial names. His initial solution
was to call the groups varieties. Later, in recognition of the
genetic isolation of the varieties, he changed the designa-
tion to a newly invented term, "syngen." Finally, as more
became known about the syngens, particularly their isozymes,
responses to different strains of killers, fission rate, and
other traits, Sonneborn recognized the syngens of Parame-
cium aurelia as separate species and designated them P.
primaurelia, P. biaurelia, and so on. In other less-well-charac-
terized ciliates, the mating groups are still called syngens.
Sonneborn also pointed out that the sibling species of
the P. aurelia group, as well as the sibling species of other
protozoans that are delimited primarily by their mating types,
presented a set of interesting ecological and evolutionary
problems. He noted that some species in the P. aurelia group
have a long immature period after conjugation, while oth-
ers have a very short or no immature period. Since those
with a long immature period are less likely to mate with
each other in nature, he classified them as "outbreeders,"
while those with a short immature period he classified as
"inbreeders." Outbreeding, which favors genetic diversity,
was held to be the ancestral type. He made detailed studies
of the properties of the various species and also studied the
viability of progeny obtained from crosses. He related this
information to the ecology and evolution of the croups.
GENE S
0 1
Different Mendelian genes were not readily found in Para-
mecium, but the behavior of the first ones that Sonneborn
found were sufficient to establish the validity of the com
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TRACY MORTON SONNEBORN
287
plex cytological events of the life cycle. Eventually, it was
fount! that numerous mutants conic! be isolates! after chemical
mutagenesis. Sonneborn then engages! in a large stucly, iso-
lating more than 100 different visible morphological en c!
behavioral mutants. These were then testec! for linkage. Be-
cause of the large number of chromosomes in Paramecium
en c! perhaps because of a high rate of recombination, few
cases of linkage en c! no maps resultecI.
TRICHOCYSTS
Sonneborn's last project was the investigation of an aber-
rant mutation that reclucec! the ability of trichocysts to clis-
charge. Although several simple gene mutations hac! the
same effect, this mutant seemec! to follow the cytoplasm in
crosses. A more cletailec! analysis revealer! that it was inher-
itec! just as mating type was inheritec! in many strains that
is, it was macronuclear inheritance as clescribec! above. Since
Sonneborn's cleath, aciclitional cases of macronuclear in-
heritance affecting other traits have been fount! en c! are
now being actively investigated.
CONCLUSION
While Sonneborn was learning whatever Paramecium conic!
teach him about biology, a new generation of microbial
geneticists, working with fungi, bacteria, and bacterioph-
ages, was establishing the foundations for the new science
of molecular biology. Unlike Paramecium, these organisms
hac! properties that prover! to be invaluable in the new sci-
ence. They had simple nutritional requirements, synthesiz-
ing most of the complex substances they neeclec! en c! thereby
enabling the investigator to study the genetic control of
many of the enzymes of metabolism. They conic! be plater!
onto agar, making possible the quick en c! easy examination
of innumerable clones. This technique was absolutely es
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288
B I O G RA P H I C A L
EMOIRS
sential for the study of mutations or rare recombinants. In
these organisms one could carry out studies on the role of
genes in controlling metabolic pathways, enzyme synthesis,
and enzyme structure. Investigations of mutations and ge-
netic fine structure also were possible. These were the stud-
ies that finally led to our knowledge of the roles of DNA
and RNA and produced the modern revolution in molecu-
lar biology. Paramecium was eminently unsuited for any of
these studies.
Hence, Sonneborn did not participate in this revolution
that was sweeping biology and biochemistry, although it
was clear that, like everyone else, he greatly appreciated
and admired the work that was going on. He would have
loved to be at its forefront. But Paramecium did not lead
him there and could not have led him there, for it was
simply not useful for such studies. The Nobel prizes that
were awarded so generously to the disciples of the new biol-
og,v eluded Sonneborn. That is not to say that his work was
unnoticed. He was, indeed, widely recognized as an out
standing investigator. Nevertheless' a glance at anv current
.1 ~· ~. · ~
-7 -- a------- --- ----I
textbook of general biology or genetics leads one to the
conclusion that he was not the originator of concepts that
are basic to the thinking of most biologists and geneticists
today.
It has been suggested that Sonneborn avoided more con-
ventional genetics and focused on the role of the cytoplasm
in heredity. In my view, that notion is not correct. Sonneborn
concentrated on the inheritance of whatever traits he could
find in Paramecium without prejudice. It simply turns out
that most of the easily observable traits in Paramecium are
inherited in a non-Mendelian fashion. Would he have pur
sued his research differently had he known that Paramecium
could not take him to the forefront of the great revolution
in biology that was just developing? In those early days no
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TRACY MORTON SONNEBORN
289
one knew what Paramecium hac! to offer. It was a member of
a group of organisms that was simply too big en c! too cliffer-
ent to be left unexplorecI. We hac! to know what protozoa
were like, just as we hac! to know about bacteria en c! viruses
en c! insects en c! mice en c! corn en c! worms en c! zebra fish.
We hac! to know about the role of the cytoplasm in genet-
ics. Anti, incleecI, Paramecium turner! out to be icleal for the
stucly of inheritance at the cellular level en c! for the stucly
of nuclear differentiation. Although there are no plasma-
genes, there are cytoplasmic entities that contain DNA. There
are stable metabolic states that are passer! from one genera-
tion of cells to the next. Preexisting structures en c! patterns
of structures are important in determining new structures
at cell division. Anti, finally, differentiation of new nuclei in
ciliates can produce new stable configurations en c! can be
influencec! by factors emanating from preexisting nuclei
en c! passer! through the cytoplasm. The role of preexisting
structure in clevelopmental biology is not yet unclerstoocI,
ant! the strange nuclear ant! cytoplasmic effects that
Sonneborn uncoverec! are still unexplainec! at the molecu-
lar level. Whatever the final outcome of studies of these
phenomena, he must take his place among the most bril-
liant and devoted experimentalists in the history of biology
en c! a true giant, like no other, in the field! of protozoan
research.
~ HAVE DRAWN ON unpublished material in my files, much re-
ceived from Tracy himself over the years, as well as unpublished
material from Ruth Dippell and Ruth Sonneborn, his wife. The
reader is also referred to an account of Tracy's life by G. H. Beale
in Biographical Memoirs of Fellows of the Royal Society, vol. 28, pp. 537-
74 (London: Royal Society, 1982~.
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290
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S E L E C T E D
EMOIRS
B I B L I O G RAP H Y
1930
Genetic studies on Stenostomum incaudatum (nov. spec.), II. The ef-
fects of lead acetate on the hereditary constitution. 7. Exp. Zool.
57:409-39.
1932
Experimental production of chains and its genetic consequences in
the ciliate protozoan Colpidium campylum. Biol. Bull. 63:187-211.
1937
Sex, sex inheritance and sex determination in Paramecium aurelia.
Proc. Natl. Acad. Sci. U.S.A. 23:378-85.
1939
Paramecium aurelia: mating types and groups; lethal interactions;
determination and inheritance. Am. Nat. 73:390-412.
1941
Relation of macronuclear regeneration in Paramecium aurelia to ma-
cronuclear structure, amitosis and genetic determination. The Collecting
Net 16:3-4.
Sexuality in unicellular organisms. In Protozoa in Biological Research,
ed. G. N. Calkins and F. M. Summers, pp. 666-709. New York:
Columbia University Press.
1943
Gene and cytoplasm. I. The determination and inheritance of the
killer character in variety 4 of P. aurelia. Proc. Natl. A cad. Sci.
U.S.A. 29:329-38.
Gene and cytoplasm. II. The bearing of the determination and in-
heritance of characters in P. aurelia on the problems of cytoplas-
mic inheritance, Pneumococcus transformations, mutations and
development. Proc. Natl. Acad. Sci. U.S.A. 29:338-43.
1945
Gene action in Paramecium. Ann. Mo. Bot. Garden 32:213-21.
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TRACY MORTON SONNEBORN
1946
291
Experimental control of the concentration of cytoplasmic genetic
factors in Paramecium. Cold Spring Harbor Symp. Quant. Biol. 11 :236-
55.
1947
Recent advances in the genetics of Paramecium and Euplotes. Adv.
Genet. 1:263-358.
1948
The determination of hereditary antigenic differences in genically
identical Paramecium cells. Proc. Natl. Acad. Sci. U.S.A. 34:413-18.
With A. LeSeur. Antigenic characters in Paramecium aurelia (variety
4~: determination, inheritance and induced mutations. Am. Nat.
82:69-78.
1950
Methods in the general biology and genetics of Paramecium aurelia.
7. Exp. Zool. 113:87-148.
Beyond the gene two years later. In Science in Progress, ed. G. A.
Baitsell, pp. 167-203. New Haven: Yale University Press.
1954
The relation of autogamy to senescence and rejuvenescence in P.
aurelia. f. Protozool. 1:36-53.
1957
Breeding systems, reproductive methods, and species problems in
protozoa. In The Species Problem, ed. E. Mayr, pp. 155-324. Wash-
ington, D.C.: American Association for the Advancement of Sci
ence.
1959
Kappa and related particles in Paramecium. Adv. Virus Res. 6:229-
356.
1962
Does preformed cell structure play an essential role in cell hered
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292
B I O G RA P H I C A L
EMOIRS
ity? In The Nature of Biological Diversity, ed. T. M. Allen
221. New York: McGraw-Hill.
1965
,, pp. 165
With T. Beisson. Cytoplasmic inheritance of the organization of the
cell cortex in Paramecium aurelia. Proc. Natl. A cad. Sci. U.S.A. 53:275-
82.
1970
Methods in Paramecium research. In Methods in Cell Physiology, vol. 4,
ed. D. Prescott, pp. 241-339. New York: Academic Press.
1974
Paramecium aurelia. In Handbook of Genetics, vol. II, ed. R. King, pp.
469-594. New York: Plenum Press.
1975
The Paramecium aurelia complex of fourteen sibling species. Trans.
Am. Micros. Soc. 94:155-78.
1977
Local differentiations of the cell surface of ciliates: their determina-
tion, effects and genetics. In The Synthesis, Assembly and Turnover
of Cell Surface Components, ed. G. Poste and G. L. Nicholson, Cell
Surface Reviews, vol. 4, pp. 829-56. New York: Elsevier/North Hol-
land.
1979
With M. V. Schneller. A genetic system for alternative stable charac-
teristics in genomically identical homozygous clones. Dev. Genet.
1:21-46.
1980
With Y. Brygoo, A. M. Keller, R. V. Dippell, and M. V. Schneller.
Genetic analysis of mating type differentiation in Paramecium tetraurelia
II. Role of the micronuclei in mating-type determination. Genet-
ics 94:951-59.
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Representative terms from entire chapter:
morton sonneborn
