(b. Hamburg, Germany, 30 August 1902; d. Sacramento, California, 23 October 1981)
Curt Stern was the son of a businessman. Barned Stern, and his wife, Anni, a schoolteacher. He grew up in Berlin during World War I. During the war his father, a British citizen, was interned. Stern graduated from gymnasium in 1918 at the age of sixteen, which was not unusual during the war years since it enabled young men to join the army two years earlier than normal. However, since the war ended before Stern could be drafted, he went immediately on to study zoology at the University of Berlin. He did his doctoral work under the great protozoologist and general biologist Max Hartmann, who was a member of the Kaiser Wilhelm Institute (KWI) and an honorary professor at the university. Stern received his Ph.D. with a cytological thesis on the mitosis of a heliozoan in 1923, at the age of twenty-one, an unusually early age even for boys who had graduated early from gymnasium. At that time the Rockefeller Foundation started a program of international fellowships and Stern was one of the first recipients. In 1924 he went to Columbia University to work with T. H. Morgan in the famous “fly room,” where the linear arrangement of genes in the chromosomes of Drosophila had been discovered and where work on chromosomal genetics was progressing very fast. Stern worked in this group with enthusiasm, learned the methods used in the genetics of Drosophila, and published his first Drosophila paper together with C. B. Bridges; it established the order of genes in the extreme left end of the second chromosome. Drosophila remained the main object of Stern’s research, to which he later added human genetics.
In 1926 Stern returned to Germany and became an assistant at the KWI in the department of Richard Goldschmidt. His duties were not onerous; he mainly helped Goldschmidt in proofreading his influential book Physiologische Theorie der Vererbung. Otherwise he was free to pursue his own research, working out the problems he had started at Columbia. In 1931 Stern married Evelyn Sommerfield, whom he had met in 1925 while he was working in Morgan’s lab. They had three daughters. In 1932 he won a second Rockefeller Fellowship and again went to Morgan’s lab, which in the meantime had been moved to the California Institute of Technology at Pasadena. When Hitler came to power in 1933 Mrs. Stern, who was an American citizen and not in danger, went to Germany to find out whether it was safe for her husband to return. His friends advised against it, and Stem immediately set out to find a position in the United States.
At that time the University of Rochester in Rochester, New York, was in the process of developing from a small liberal arts college into a major university. The noted embryologist Benjamin Willier had been appointed chairman of the biology department and had started to build up the department. He appointed Stem a research associate in 1933, and in 1935 Stem joined the teaching faculty as an assistant professor. In 1940 Willier left Rochester and Stern was appointed acting chairman. In 1941 he was named chairman of the department of zoology and of the division of biological sciences and full professor. In 1947 he became professor of zoology at the University of California at Berkeley, succeeding his former boss, Richard Goldschmidt, who had just retired. In 1958 Stem was also appointed professor of genetics at Berkeley. He retired in 1970, suffering from the beginning stages of Parkinson’s disease. His last public address was the presidential address at the Thirteenth International Congress of Genetics at Berkeley, which he delivered against the advice of his physicians. The address was an inspiring event, impressive in its enthusiasm and love for research. Stern died of cardiac failure.
During his stay at Columbia, Stern worked on several topics in Drosophila but became particularly interested in the function of the Y chromosome. He found that the X--linked gene bobbed (bb, short bristles) has an allele in the Y chromosome. Thus an XbbO male (a male carrying one X marked by the gene bb and no Y) is phenotypically bobbed, while a Xbb/Y+ male is normal; an Xbb/Xbb/Y+ female also has normal bristles. He found in addition that the Y chromosome can contain a mutated bb allele, so that a male xbb/Ybb is bobbed. XO animals are sterile males, and one fragment of the Y chromosome attached to the X chromosome does not restore fertility; but two or three fragments can do so. Stern had then proved, by a combination of genetic and cytological techniques, that the Y chromosome carries an allele of the bb gene and two or more genes that are needed for fertility. Previously it had been assumed that the Y chromosome is genetically empty; the demonstration of genes in the Y therefore constituted a major discovery.
The presence of bb alleles on the X and Y chromosomes was used for a further study of much broader implications. It permitted Stern to study the effect of different doses of alleles at the bobbed locus on bristle length. He had at his disposal five bb alleles: + in the X and Y chromosomes, and a standard bb in both chromosomes, and in addition bb1, an extreme allele that is lethal in homozygous and hemizygous condition but in compound with a standard bb (bb/bb1) results in very short, fine bristles. These five alleles could be tested in hemizygous condition (XO males) in homozygotes and heterozygotes in diploid males and females, triploid males and females, and superfemales (normal females trisomic only for the X chromosome) and tetraploid females (XXYY). The result was simple. The interaction of bb alleles is in all cases additive: One bb allele (XbbO male) causes shorter bristles than two alleles (Xbb/Xbb females and Xbb/Ybb males), and still larger bristles are present in triploid females (Xbb/Xbb/Ybb). In triploid males the bristles were even of normal length (XbbYbbYbb). The lethal allele and a further allele that arose by mutation are weaker than standard bb. Thus all bobbed alleles act in an additive way toward the production of the normal phenotype.
This principle of additive action of alleles of the bb locus has had great importance for the theory of gene action. It was taken as supporting Gold-schmidt’s quantitative theory of gene structure and gene action, though it was not involved in its original conception. It has been demonstrated for other genes, but in other cases genes have been shown to act in a different direction, higher doses producing a more mutant phenotype. It later turned out that bobbed is in many respects a special type of gene. In 1968 Ritossa, Atwood, and Spiegelman showed that the bobbed locus is identical with the nucleolar organizer whose primary gene product is ribosomal RNA. The ribosomal DNA gene is a long tandem repeat, now known to consist of two alternating coding sequences and spacers. The bobbed mutations are loss mutations in which part of the ribosomal DNA is lost; thus fewer ribosomes are present and less protein is produced in bb cells, resulting, among other phenotypes, in short, slender bristles. Thus the bobbed mutations are true quantitative mutations, while most mutations have qualitatively different gene products as their primary effects.
Another project started at Columbia dealt with the cytological basis of genetic recombination. Morgan and his collaborators, basing their work on the chiasmatype theory of F. A. Janssens (1909), interpreted crossing-over of genes as due to physical exchange of parts of chromosomes, the breakage-and-reunion mechanism. Goldschmidt had proposed a different mechanism of crossing-over, and Stern, who as a graduate student had studied the literature on crossing-over thoroughly, wrote an unpublished critical review of Goldschmidt’s ideas and decided to test the breakage-and-reunion theory directly. The way was shown in Karl Belar’s 1923 paper on the meiosis of the heliozoan Actinophrys sol. In this paper Belar states that breakage-and-reunion can be demonstrated only if two homologous chromosomes are cytologically distinguishable from each other and from the normal chromosome.
Stern, with this idea in mind, searched, during his stay at Columbia, for such cytologically distinct chromosomes. He found one X chromosome to which the long arm of the Y chromosome had been attached at the proximal end. But he had to wait for two years until he obtained a second usable chromosome. In 1928 H. J. Muller found that X rays could induce not only mutations but also chromosomal rearrangements. He sent Stern several of these, and Stern chose for his experiments a translocation called Bar-of-Stone. In this translocation the distal third of the X chromosome is translocated to the small fourth chromosome, so that the X chromosome appears only two-thirds its normal length and is marked by the dominant gene Bar (reduced size of the eye). Another gene, the recessive eye-color gene carnation, was introduced into the X chromosome marked by the long arm of the Y chromosome, so that Stern now had two chromosomes that differed both in chromosomal structure and in genetic makeup. He looked in the progeny of females heterozygous for these two chromosomes for recombinant males, that is, males with completely normal eyes, or males that had Bar eyes of carnation color. These recombinants were investigated cytologically and found to have either normal X chromosomes or short X chromosomes carrying the arm of the Y chromosome. This correlation between genetic and cytological recombination established the breakage-and-reunion theory since crossing-over is accompanied by the exchange of chromosome parts. A similar proof was given at the same time for chromosomes of maize by Harriet Creighton and Barbara McClintock.
Even though this proof was accepted among geneticists, it was regarded as “anticlimactic” by L. C. Dunn in his A Short History of Genetics because the breakage-and-reunion theory appeared to be already well established by the large amount of genetic data accumulated by Morgan and his group, and Stern (1971) agreed with him. It was, however, an important contribution because alternative interpretations of recombination continued to appear. One of these was put forth at about the time of Stern’s work by the botanist Hans Winkler. He proposed a mechanism called “conversion” that assumed that genes in heterozygous condition are more likely to mutate to the other allelic state than they are in homozygotes, thus producing the illusion of exchange of parts. Stem reviewed Winkler’s book critically (1930) and Winkler answered with a coun-tercritique. But the weight of Stern’s experiments was so strong that breakage-and-reunion remained the established theory for twenty-five years. In 1955 Mary Mitchell obtained segregations in the fungus neurospora that were incompatible with a simple breakage-and-reunion mechanism, and that she called “conversion”, but not in the sense of Winkler, While Winkler had used the analogy to mutation, Mitchell proposed an error in copying DNA, the newly synthesized copy switching from one strand of DNA to the other, the copy-choice mechanism. For some years the question of breakage-and-reunion versus copy-choice was widely debated in the genetic literature. Only thirty years after Stern’s experiments was breakage-and-reunion established at the DNA level in bacteriophage lambda by Meselson and Weigle (1961). They used DNA strands labeled by heavy isotopes and differing in two genes. The experimental design is thus exactly the same as that used by Stern.
A final project started during Stern’s stay in the fly room at Columbia was the demonstration of somatic crossing-over. Crossing-over was at that time well known to occur during meiotic division but was not suspected to occur in mitotic division. The work started from the observation made by Bridges (1925) that females heterozygous for an X chromosome-linked recessive gene and a dominant Minute gene, actually a small deletion causing small bristles and rough eyes, occasionally showed non-Minute recessive patches. Stern (1927) established the same phenomenon for autosomal genes and Minutes. This mosaicism was originally interpreted as being due to loss of the Minute-carrying chromosome. Stern investigated this mosaicism extensively, starting at Columbia and continuing at Dahlem, Pasadena, and Rochester.
In 1936 he published his findings and conclusions. The hypothesis of chromosome loss due to the presence of Minutes was rejected because mosaicism also occurs rarely in the absence of Minutes—Minutes only increase the frequency of mosaics—and because a Minute gene could have a similar effect if present in a chromosome other than that carrying the recessive. The decisive observation was made on females that carried the sex-linked genes yellow (bristles) and singed (bristles) on opposite chromosomes. In these the mosaics appeared sometimes in the form of twin spots containing adjacent areas where the bristles were yellow of normal shape and singed of normal color. This phenomenon was called “somatic segregation” and Stern proposed that it may be due to rare crossing-over between the homologous chromosomes at mitosis. He showed through models that crossing-over between two genes would lead to single spots, but crossing-over closer to the centromere than the more proximal gene would lead to twin spots. Stern could show that somatic crossing-over occurs between two strands at the four-strand stage. The recombination values between specific genes are different from those obtained at meiosis: somatic crossing-over is most frequent close to the centromere and becomes increasingly rare removed from it. In order to establish somatic crossing-over more convincingly, Stern carried out a number of further experiments using chromosome rearrangements together with recessive marker genes; all agreed with the expectations from the theory. Stern cautioned that the theory of mosaic formation by somatic segregation, caused by somatic crossing-over, was not yet proven. But it succeeded so well in explaining all the unexpected phenomena observed, some of which are quite complicated, that the theory was immediately accepted by all geneticists.
This acceptance has remained to the present day. Somatic segregation is routinely used in the study of developmental effects of genes. This use was actually introduced by Stern himself and is still widely employed. Another problem in which somatic crossing-over has been useful is the mapping of genes on the chromosomes, particularly in organisms that have no sexual stages and therefore no meiosis, such as the fungus Aspergillus.
Stern’s classical paper on somatic crossing-over represents the last paper in the series of genetic-cytological investigations that had been started during his Rockefeller fellowship at Columbia. He turned now to other topics, most of which had as their goal the elucidation of gene action. This problem had already been raised in his work on the bobbed alleles. It now became the main focus of his attention. The first technique he used was organ transplantation in larvae of different genotypes. The structures the grafts form in the adult are scored for the gene-controlled characters. This technique had been introduced into genetics by Caspari in the moth Ephestia (1933) and had just been adapted by Beadle and Ephrussi to the study of eye pigments in Drosophila (1936). The technique permits the distinction between autonomous genes, in which each cell develops the character determined by its own genotype, independently of the genotype of the remainder of the organism, and “nonautonomous” genes, in which the phenotypes of host and graft influence each other. In these studies he was joined by the Swiss embryologist Ernst Hadorn, who was spending the year 1936–1937 in Rochester as a Rockefelier Fellow.
The first character investigated by the transplantation method was the sterility of XO males. It turned out to be autonomous. The next character was the pigmentation of the testes, which is suppressed in some eye color mutants. If the implanted testis remained free in the body cavity, no influence of the host was found. But if it became attached to the host’s sperm ducts, which develop independently of the testis and in the pupal stage fuse with it, pigmented spots appeared on the colorless testis or sperm duct. This is due to migration of epithelial sheath cells between the testis and the sperm ducts. In a final project Stern investigated the difference in shape between different Drosophila species. In many Drosophila species the testes are coiled tubules. They arise from an elliptical larval testis that in late pupal stages grows out at the posterior end, without cell division. The outgrowth proceeds at different rates on the two sides, leading to a coiled structure. But in some species, such as Drosophila pseudoobscura, the testis does hot grow out strongly and remains elliptical. Transplantation between species with coiled and uncoiled testes showed that the coiling is induced by the sperm ducts that fuse with the testis and that are themselves coiled in the opposite direction. It appears that the sperm duct releases a growth-promoting substance. Also, different species may show different degrees of coiling, for example, two to three coils in Drosophila melanogaster as opposed to four coils in Drosophila virilis. This difference is also due to the genetic constitution of the inductor, the vas deferens, and not the constitution of the testis itself. This is the only example of a genetic influence on an inductor. In all other cases of differences in induction described in the literature, the differences are due to differences in the competence and norm of reaction of the reacting tissue, while the inducer is remarkably constant in evolutionary history.
When he had finished these transplantation experiments Stern embarked on a very ambitious project, the study of the position effect. The position effect was, and still is, regarded as one of the great unsolved problems of genetics. This project was associated with a change in Stern’s style of research. Due to his rising reputation. Stern began to attract graduate students and postdoctoral research associates. He had had one Ph.D. student in Germany, Ursula Philip, who later went to England and worked with Haldane. In Rochester he began to attract the first in a long series of Ph.D. students. His first students were James V. Neel and Harrison Stalker, both of whom became prominent geneticists. Stern’s last collaborator, C. Tokunaga, estimated that during his lifetime Stern trained about thirty Ph.D.s. Several of them made major contributions to science in their own research and perpetuated Stern’s influence on the younger generation of scientists. In addition, since his collaboration with Hadorn, Stern almost continually had research associates and postdoctorals associated with him, so that he became the leader of a team. This change in the style of research was to a certain degree general, since beginning with World War II large amounts of funds for research from government sources became available.
Stern’s collaborators on the position effect worked in two areas: Gertrude Heidenthal and Elizabeth W. Schaeffer participated in the genetic work, while Robert MacKnight and, after his untimely death, Masuo Kodani carried out cytological investigations on the salivary gland chromosomes to determine the position of the breaks in translocations. The project was very carefully prepared and designed. Stern chose the gene cubitus interruptus (cubitus is a vein on the wing). The gene appeared suitable because several mutants were known, its phenotypic effect could be expressed quantitatively, a position effect for this gene had been demonstrated by Dubinin and Serebrovskii, and the gene was located in the small fourth chromosome, which in single, double, and triple dose gives rise to viable animals. It was thus possible to compare mutant and wild-type alleles in homozygotes and heterozygotes in haploid, diploid, and triploid conditions; in addition, a deletion for the gene was available. The quantitative possibilities were thus parallel to the earlier work on bb.
In analogy to bb, most ci alleles were shown to act additively toward the production of a normal vein. Stern showed that different wild-type alleles could be distinguished by their effect in heterozygotes at different temperatures, a phenomenon to which the term “isoalleles” was applied. One ci allele, ciw, is different from others in that it is more abnormal in the homozygous than in the hemizygous condition, showing that this allele does not act toward normality but toward the abnormal condition antagonistic to the wild type. Still harder to explain are the interactions of ci alleles with the fourth chromosome deficient for the ci gene: The deficient fourth chromosome also acts toward normality. These results led Stern to abandon the hypothesis of simple additivity and instead propose a more complex model: The primary reaction of a gene consists in conversion of a “substrate” to a “product”. Each allele has not only a characteristic efficiency in transforming “substrate” into “product” but also a characteristic combining power for the “substrate”. The different alleles in a diploid and triploid organism compete for a limited amount of substrate, so that the final amount of “product” depends not only on the efficiency of the allele itself, but also on the combining power and efficiency of the other alleles present in the same genome.
This ingenious hypothesis was, however, insufficient to interpret the position effects. Stern and his collaborators produced nineteen chromosomal rearrangements of the wild-type allele of ci and fifty-five rearrangements involving the mutant alleles. Their phenotypic effects were tested in compounds with normal and mutant alleles in their normal positions. Stern could exclude the possibility that the position effect is due to a disturbance of somatic pairing of chromosomes or to a closeness to particular chromosomal structures in their new location, but a general conclusion encompassing all observed facts remained elusive. In his last paper of the series (Stern and Kodani 1955) Stern writes, “This lack of correlation in effects points to qualitative differences in the developmental reactions of the different R(ci) alleles or their products”, and “No deeper insight into the mechanism of position effect at the ci locus can be presented”.
Stern was obviously disappointed in this outcome of a large and well-conceived project; he mentions it only briefly in his memoirs of his scientific career (1971, 1974) and cites only the discovery of isoalleles as a positive result. But it is still the most thorough investigation of a position effect ever attempted, and the lack of a clear-cut result may very well be due to the fact that there is no general rule for the behavior of position alleles, or that the rule cannot be seen at the chromosomal level but only at the DNA level. Attempts to analyze position effects (not the ci effect, though) at the DNA level are in progress but have not yet led to generalized models either.
Parallel with this project Stern directed a major study on the mutagenicity of X rays at low dosages. During these years the Manhattan Project was organized by the U. S. Army, and the University of Rochester was chosen to investigate all biological aspects important for the use of atomic energy for war as well as for peacetime purposes. The genetic division of this project was led by Donald R. Charles, but Stern took over the direction of the Drosophila work in collaboration with Warren P. Spencer, Ernst Caspari, and Delta Uphoff. Spencer and Stern demonstrated that the straight relationship between radiation dose and mutation rate was valid down to 25r. But experiments designed to test the effect of low-level radiation over an extended span of time led to contradictory results. Since the experiment involved irradiation of sperm stored in the spermatheca of a female for up to three weeks, and since it is known that aging of sperm induces mutations, it is possible that the mutagenic effect of radiation is not simply superimposed on the aging effect but is subject to a more complex interaction.
A by-product of this work was a large collection of X chromosome-linked lethal mutations, most of them spontaneous. Stern, in collaboration with Ed Novitski and others, used this collection to study a problem that was at that time much discussed by evolutionists: whether heterozygotes may be superior in fitness to the dominant, wild-type homozygotes. Stern and his collaborators tested heterozygotes for thirty-six spontaneous lethals and thirty-nine lethals derived from exposure to 50r low-intensity gamma rays for viability and found that their ability to survive varied. On the average, the viability of heterozygotes for lethals was slightly lower than that of normal homozygotes (0.965:1.000), but some heterozygotes had definitely reduced viability, up to almost half that of the wild-type homozygotes, while others were definitely superior to the normal homozygotes, a phenomenon designated as heterosis.
During his time in Rochester, Stern started yet another project, which he continued all his life: work in human genetics. This interest grew out of his teaching activities. It started out with a graduate student seminar in some problems of human genetics. There followed an undergraduate course in the subject for nonbiology majors and without prerequisites in biology. The course became known as a very valuable one and was made obligatory for sociology majors. While the course had no prerequisites, it was very exacting. Stern presented the usual contents of a genetics course—Mendelian rules, linkage, and chromosome mechanics—as facts, but he derived the foundations of population genetics, breeding patterns, human mutation rates, and inbreeding quantitatively and required students to become well acquainted with the algebraic techniques used in these problems. It must have required a great amount of work to organize this course because Stern had to study the extensive literature on human genetics and become acquainted at first hand with the mathematical methods he was using. His fresh insight enabled him to present these matters simply and clearly. For example, his derivation of the Hardy-Weinberg law is the simplest and most convincing one I have ever seen.
One difficulty for this course was the lack of a suitable textbook. There were several textbooks of human genetics, but they were restricted to presentations of factual data in the form of pedigrees, mostly of rare diseases, and in their theoretical part pointed to the importance of eugenics, a movement which was still strong at the time. Therefore, Stern published a textbook, Principles of Human Genetics (1949), which caught on only slowly since few biologists were prepared to teach such a course. But after a short time it became popular, went through three editions, and was translated into seven languages. It now has a special position among the books on human heredity.
Stern attacked several research programs in human genetics and became a highly respected authority on human genetics. Among his projects the subject on which he published most was an investigation of genes in the human Y chromosome, reminiscent of the Drosophila problem several decades earlier. The method here was different, however. He investigated several cases in which genes, on the basis of pedigrees, had been regarded as Y-linked. He found that in all cases the basis for the claim was weak, and much of the evidence was derived from stories of patients and not from direct observation. Many of the early human pedigrees had been obtained in a similar manner, and Stern emphasized that genetic hypotheses should be based only on direct observations by the investigator. One case in question concerned the occurrence of hair on the outer rim of the ear. The patient who first showed the trait claimed that all his male relatives had it, but since the man was old and mentally disturbed, and no further confirmation was offered, Stern felt safe to reject the claim. Around the same time some pedigrees from India seemed to bear out the hypothesis that hairy ears were indeed due to a gene carried in the Y chromosome. Stern went to India and together with W. R. Centerwall and S. S. Sarkar collected pedigrees himself. While the data seemed to support a Y-linked inheritance, Stem remained skeptical because difficulties of ascertainment and some other irregularities of expression made it impossible to exclude autosomal dominant inheritance. In the meantime other workers collected similar pedigrees. The results were the same but several authors interpreted them as clear evidence of Y linkage. The resulting controversy did not clear up the matter. Stern was inclined to believe that Y linkage was the most likely explanation, but he preferred to remain cautious.
In the last twenty years of his active scientific life Stern concentrated on the problem of pattern formation. In this work Aloha Hannah-Alava, Chiyoko Tokunaga, and a large number of graduate students were associated with him. He studied the pattern of bristles on the surface of Drosophila and the sex combs on the legs of males, and a large number of genes influencing these structures. The method involved the use of genetic mosaics produced either by loss of one X chromosome or by somatic crossing over in genetic heterozygotes. Genetically mutant patches produced in this way on a genetically wild-type background could behave in either one of two ways: they could develop autonomously so that the mutant areas show the mutant phenotype, or they could show the wild-type phenotype of the background, that is, develop in a nonautonomous way. He interpreted the data according to a model by which underlying the visible pattern is “a system of patterned singularities” or “prepattern”, a term introduced by Karl Henke, on which the cuticle reacts with the formation of bristles or sex combs. Most mutant patches turned out to behave in an autonomous way, suggesting that the genes involved affect the ability of the reacting structures to respond to the prepattern. But one gene-controlled aberration, the increase in number of sex combs in males of the mutant “eyeless-dominant”, behaved in a non-autonomous way and was therefore regarded as affecting the prepattern itself. In this mutant the growth pattern of the leg segment is abnormal and this seems to affect the structure of the prepattern.
The reports of his experimental research do not comprise the whole of Stern’s publications. He became interested in the history of genetics and edited with Eva Sherwood a book on Gregor Mendel and the rediscovery of his work. In his systematic study of human genetics he found that the fundamental expression of population genetics, at that time known as Hardy’s law, had been discovered at the same time by the German physician Wilhelm Weinberg, and he was able to change the established name to the Hardy-Weinberg law. He was concerned about public affairs and spoke out on his opinions, but always within the borders of his special competence. He was one of the first to express concern about the danger of exposure to radiation for human populations and the future of mankind. He also had an interest in philosophy and ethics and published a number of philosophical essays.
In his relations with his colleagues, students, and friends Stern was friendly, pleasant, and always ready to help with advice and action. He had the luck early in life to become closely acquainted with the present and future leaders in his field. In his year at Columbia he was associated with the leaders of genetics (Morgan, Sturtevant, and Bridges); in Germany the KWI was the center of genetic research and Stern came to know closely the leading geneticists of Germany (Correns, Goldschmidt, and Hartmann) as well as the younger group of biologists at KWI (Belar, Hämmerling, Holtfreter, and others). He formed strong and lasting friendships with many of these colleagues. Stern was therefore in the unique position of knowing both the American and the German traditions in genetics and of combining these influences in a unique and original way.
While his manner was always friendly and polite, there was a very strong character under the smooth surface. Stern was fundamentally serious, and had high expectations for himself and his fellow humans. He had much determination and willpower and pursued his goals with perseverance and a strong sense of duty. He worked constantly and with great concentration, but in an unhurried and relaxed way. To his students he was kind and tolerant of minor lapses and faults, but he was exacting as far as their work was concerned and did not tolerate sloppy work. He was highly esteemed by his colleagues and former students and therefore had an enormous influence not only on the progress of genetics but also on the attitudes and opinions of his fellow scientists. Stern’s devotion to his science and his loyalty to his friends were widely appreciated, and he was generally regarded as a wise, humane, and upright human being in addition to being an outstanding scientist.
I. Original Works.“Ein genetischer und cytologischer Beweis für Vererbung im Y-Chromosom von Drosophila melanogaster”, in Zeitschrtfi für induktive Abstammungs und Vererhungslehre, 44 (1927), 187–231; “Fortschritte der Chromosomentheorie der Vererbung”, Ergebnisse der Biologie4 (1928), 205–359; “Über die additive Wirkung multipler Allele”, in Biologisches Zentralblatt, 49 (1929), 261–290: “Konversionstheorie und Austauschtheorie”, ibid., 50 (1930), 608–624; Multiple Allelie (Berlin, 1930): Faktorenkoppelung and Faktorenaustausch (Berlin, 1933); “Somatic Crossing-Over and Segregation in Drosophila melanogaster,” in Genetics, 21 (1936), 625–730; “The Determination of Sterility in Drosophila Males Without a Complete Y-Chromosome”, in American Naturalist, 72 (1938), 42–52, written with Ernst Hadorn; and The Relation Between the Color of Testes and Vasa Efferentia in Drosophila in Genetics, 24 (1939), 162–179, written with Ernst Hadorn.
“The Growth of Testes in Drosophila, I. The Relation Between Vas Deferens and Testis Within Various Species”, and “II, The Nature of Interspecific Differences, in Journal of Experimental Zoology, 87 (1941), 113–158, 159–180; “Genic Action as Studied by Means of the Effects of Different Doses and Combinations of Alleles”, in Genetics, 28 (1943), 441–475; The Hardy-Weinberg Law”, in Science, 97 (1943), 137–138; “On Wild-type Iso-alleles in Drosophila melanogaster”, in Proceedings of the National Academy of Sciences of the United States of America, 29 (1943), 361–367; “The Journey, Not the Goal”, in Scientific Monthly, 58 (1944), 96–100; “The Effects of Changes in Quantity, Combination, and Position of Genes”, in Science, 108 (1948), 615–621; “Experiments to Test the Validity of the Linear R-dose/Mutation Frequency Relation in Drosophila at Low Dosage”, in Genetics, 33 (1948), 43–74, written with Warren P. Spencer; and “The Influence of Chronic Irradiation with Gamma-rays at Low Dosages on the Mutation Rate in Drosophila melanogaster, ibid., 75–95, written with Ernst Caspari.
“The Genetic Effects of Low Intensity Irradiation”, in Science, 109 (1949), 609–610, written with Delta E. Uphoff; Principles of Human Genetics (San Francisco, 1949; 3d ed., 1973); “The Sex Combs in Gynanders of Drosophila melanogaster”, in Portugaliae acta biologica, ser. A, R. B. Goldschmidt volume (1949–1951), 798–812, written with Aloha M. Hannah; “The Viability of Heterozygotes for Lethals”, in Genetics, 37 (1952), 413–449, written with G. Carson, M. Kinst, E. Novitski, and D. Uphoff; “Model Estimates of the Frequency of White and Near-white Segregants in the American Negro,” in Acta genetica et statistica medica, 4 (1953), 281–298; Two or “Three Bristles”, in American Scientist, 42 (1954), 213–247; “Studies on the Position Effect at the Cubitus Interruptus Locus of Drosophila melangogaster”, in Genetics, 40 (1955), 343–373, written with Masuo Kodani; and “The Genetic Control of Developmental Competence and Morphogenetic Tissue Interactions in Genetic Mosaics”, in Wilhelm Roux Archiv für Entwicklungsmechanik der Organismen, 149 (1956), 1–25.
“Genetics in the Atomic Age”, in Eugenics Quarterly, 3 (1956), 131–138; “Dosage Compensation-Development of a Concept and New Facts” (Fifth Huskins Memorial Lecture), in Canadian Journal of Genetics and Cytology, 2 (1960), 105–118; “New Data on the Problem of Y-linkage of Hairy Pinnae”, in American Journal of Human Genetics, 16 (1964), 455–471, written with W. R. Centerwall and S. S. Sarkar; “The Developmental Autonomy of Extra Sex Combs in Drosophila melanogaster in Developmental Biology, 11 (1965), 50–81, written with Chiyoko Tokunaga; The Origin of Genetics: A Mendel Source Book (San Francisco, 1966), edited with Eva R. Sherwood; “Nonautonomy in Differentiation of Pattern-determining Genes in Drosophila. I. The Sex Comb of Eyeless-dominant”, in Proceedings of the National Academy of Sciences of the United States of America, 57 (1967), 658–664, written with Chiyoko Tokunaga; Genetic Mosaics and Other Essays (Cambridge, Mass., 1968); “From Crossing-over to Developmental Genetics”, in Stadler Genetics Symposia, G. Kimber and G. P. Redei, eds., I/II (Columbia, Mo., 1971), 21–28; and “A Geneticist’s Journey”, in Chromosomes and Cancer, James German, ed. (New York, 1974), xii-xxv.
II. Secondary Literature. John C. Lucchesi and James V. Neel published obituaries in, respectively, Genetics, 103 (1983), 1–4, and Annual Review of Genetics, 17 (1983), 1–10.