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Section 1:Discovering Mendel

Few publications have so enduringly and variously influenced science as has the short monograph by the Augustinian monk of Brünn, Peter Gregor Mendel. Forgotten for decades, within a few years after its rediscovery it gave a mighty impetus to the doctrine of heredity; and, as Mendelism, his teaching as well as the foundation of manifold practical applications.

Hugo Iltis, Life of Mendel

Outside of Mendel Museum,photographed
by Professor Wu GuoSheng

Gregor Johann Mendel(1822-1884)


Gregor Johann Mendel (20 July 1822 – 6 January 1884) was an Austrian geneticist, meteorologist, Augustinian friar and abbot of St. Thomas' Abbey in Brünn (Brno), Margraviate of Moravia. Mendel was born in a German-speaking family in the Silesian part of the Austrian Empire (today's Czech Republic). As a young man, he studied practical and theoretical philosophy and physics at the University of Olmütz (now Olomouc, Czech Republic). Upon recommendation of his physics teacher Friedrich Franz, Mendel entered the Augustinian St Thomas's Abbey in Brünn (now Brno, Czech Republic) in 1843. He did so out of necessity and without feeling in himself a vocation for holy orders. But he soon realized that in the monastery he would be free from financial concerns and would find the best conditions for continuing his studies. In 1851, he was recommended to study in University of Vienna. Mendel studied under physicist Christian Doppler (1803-1853) and botanist Franz Unger (1800-1870) there.

Between 1856 and 1863 Mendel cultivated and tested at least 28,000 plants, carefully analyzing seven pairs of seeds and plant traits. His original idea was that heredity is particulate, contrary to the model of “blending inheritance” generally accepted at that time. His experiments with the pea plants showed that, when true-breeding different varieties were crossed to each other (e.g., tall plants fertilized by short plants), in the second generation, one in four pea plants had purebred recessive traits, two out of four were hybrids, and one out of four were purebred dominant. His experiments led him to make two generalizations, the Law of Segregation and the Law of Independent Assortment, which later came to be known as Mendel's Laws of Inheritance.

On 8 February and 8 March 1865, Mendel presented his paper "Versuche über Pflanzenhybriden" ("Experiments on Plant Hybridization") at two meetings of the Natural History Society of Brno in Moravia. It generated a few favorable reports in local newspapers, but was ignored by the scientific community. It was not until 1900 that a series of researches aimed at finding a successful theory of discontinuous inheritance (rather than blending inheritance) led to independent duplication of his work by Hugo de Vries and Carl Correns, and the rediscovery of Mendel's writings and laws.


Microscope used by Gregor Johann Mendel, photographed

by Professor Wu GuoSheng in Mendel Museum


Pea plant specimens collected in 1962, collected

by the Science Museum of Tsinghua University

Charles Robert Darwin(1809-1882)

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Charles Robert Darwin (12 February 1809 – 19 April 1882) was an English naturalist, geologist and biologist, best known for his contributions to evolutionary biology. He was the fifth of six children of wealthy society doctor and financier Robert Darwin and Susannah Darwin (née Wedgwood). His grandfathers Erasmus Darwin and Josiah Wedgwood were both prominent abolitionists. In 1825 Darwin was sent to Edinburgh University to study medicine, but he found the courses to be unbearably dull and rebelling. His father then sent him to Cambridge as a preparation for entering the Church of England as a clergyman.


After taking a poor degree at Cambridge in 1831, Darwin was at home when he received an invitation to join the Admiralty survey ship HMS Beagle, as unpaid naturalist on an expedition to chart the coastline of South America. Darwin sailed on the Beagle on 27 December 1831, and returned to England in October 1836. The five-year voyage established him as an eminent geologist whose observations and theories supported Charles Lyell's conception of gradual geological change. Evidence of geographical distributions of wildlife and fossils (especially the Galápagos results) collected from the voyage also convinced Darwin that new species are formed by the natural transformation of old ones, and over the next few years he searched for a plausible mechanism. In July 1837 Darwin started writing down his ideas at random in his Notebook on Transmutation of Species, and by September 1838, upon reading Malthus’ Essay on the Principle of Population, Darwin worked out the mechanism of natural selection. By 1856 Darwin had created a much more sophisticated theory, amassed a vast amount of supportive evidence, and had begun to write a “big book” on the topic; but the project was interrupted by the arrival of Alfred Russel Wallace’s paper in 1858. Wallace sent him an essay that described the same idea, prompting immediate joint publication of both their theories; their collaboration resulted in the famous Origin of Species.

When Darwin published his theory of natural selection, two questions still remained unanswered at that time: what is the nature of hereditary transmission between parents and offspring? And what is the nature of the origin of heritable variation? Darwin himself adopted a model of blending inheritance prevalent at his time, but the real solution to both questions had to wait until the 1920–50s, when advances in different branches of biology promoted moves towards the “Modern Synthesis” reconciling Darwin's theory of evolution and Gregor Mendel's ideas on heredity in a joint mathematical framework. Events of the modern synthesis include population genetics founded by J. B. S Haldane, Ronald Fisher, and Sewall Wright; T. Dobzhansky’s representative work; and Julian Huxley’s popularization (he coined the term “modern synthesis” in the title of his 1942 book). The process of the synthesis was long and complex because it involved the destruction of a developmental viewpoint in which the transmission of characters was thought to be inextricably connected with the mechanism by which those characters are generated in the embryo. Many modern historians would accept that it was the prevalence of this developmental model in late nineteenth-century biology, not a specific problem associated with “blending inheritance” that accounts for the widespread reluctance to take the theory of natural selection seriously during Darwin’s own lifetime.

Friedrich Miescher(1844-1885)

Friedrich Miescher was born in Basel, Switzerland in 1844. His father and uncle were both professors at Basel University and taught anatomy and physiology. Miescher initially wanted to become a priest but was opposed by his father, so he entered a local medical school and received an MD in 1868. In the autumn of 1868, he went to study at the laboratory of German physiologist and chemist Felix Hoppe-Seyler (1825-1895) at the University of Tübingen. When other scientists were debating the concept of “cell”, Hoppe-Seyler’s laboratory was already isolating the molecules that made up cells.

Hoppe-Seyler put Miescher to work on researching lymphocytes, a type of white blood cell. These cells were hard to obtain extract from the lymph glands, but they were found in great quantities in pus. Miescher collected many bandages from a nearby clinic and washed off the pus using a dilute sodium sulfate solution, and then treated them with an acidic extract of pig gastric mucosa. In 1869, he successfully isolated a new molecule from the cell nucleus and named it “nuclein”, later called nucleic acid. Hoppe-Seyler repeated his work and confirmed his discovery. Miescher published his discovery in his paper titled Ueber Die Chemische Zusammensetzung Der Eiterzellen (On the Chemical Composition of Pus Cells) in 1871. In the same year, Miescher returned to Basel and at the headwaters at the Rhine he found a more pleasant source material (compared to pus) in the sperm of the salmon. In 1872, he became the professor of physiology at Basel University.

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Hugo de Vries(1848-1935)

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Hugo de Vries (February 16, 1848 - May 21, 1935) was a Dutch botanist and a pioneer in genetics. Born as the eldest son in the family, de Vries’s father served as the prime minister of the Netherlands from 1972-1874, and his mother was a daughter of a professor in archaeology at Leiden University. From an early age, de Vries showed a keen interest in botany and studied at the Universities of Leiden, Heidelberg and Würzburg before joining the University of Amsterdam in 1877 to teach plant physiology, a career that lasted 40 years.

Influenced by Darwinian pangenesis, de Vries published Intracellular Pangenesis in 1889, which postulated that postulated that inheritance of specific traits in organisms take the form of particles, which de Vries termed as “pangenes” and 20 years later Wilhelm Johansen shortened it to gene. To support his theory of pangenes, de Vries conducted a series of experiments hybridizing various plant species in the 1890s. Unaware of Mendel's work, De Vries used the laws of dominance and recessiveness, segregation, and independent assortment to explain the 3:1 ratio of phenotypes in the second generation. But in the late 1890s, de Vries came to know Mendel's work and helped to promote it. In his own time, de Vries was best known for his mutation theory that organisms’ traits may differ significantly from the parental generation, sometimes even forming new species within one generation. Mutation theory served as the main explanatory framework in the 20th century and influenced Thomas Morgan to study mutations in the fruit fly.

Carl Correns(1864-1933)

Carl Correns  (19 September 1864 – 14 February 1933)was a German botanist and probably most famous for counting among the three re-discoverers of Mendel’s work. In 1885 Correns entered the University of Munich and studied with the renowned botanist Carl Wilhelm von Nägeli (1817–1891), with whom Gregor Mendel had corresponded with. Correns became the Extraordinary Professor at the University of Leipzig in 1902, and was appointed First Director of the newly founded Kaiser Wilhelm Institute for Biology in Berlin-Dahlem in 1913, where he had large gardens and greenhouses for experimental work at his disposal. He continued to work there in seclusion and with a very small number of coworkers until his death in 1933.


Correns showed a large interest in xenia effect, the effect of the pollen genes on the development of the fruit or the seeds. He first conducted hybridization experiments on Zea Mays (corn); after reading Mendel’s paper “Experiments on Plant Hybrids” probably in 1896, Correns studied xenia in Pisum (peas). In May 1900, Correns published his seminal paper “G. Mendel’s Rule Concerning the Behavior of Progeny of Varietal Hybrids” and focused on the complex relationships between genetic factors and character ever since. In addition to promoting Mendel as the founding figure, Correns co-discovered non-Mendelian (extranuclear) heredity at the same time with Erwin Baur in 1909.

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Erich von Tschermak(1871-1962)

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Erich von Tschermak-Seysenegg (1871–1962, here after E.T.S) was an Austrian-Hungarian botanist and agronomist. He received his doctorate from the University of Halle, Germany, in 1896. E.T.S corresponded with Hugo de Vries and Carl Correns and published his first paper in 1900. He later accepted a teaching position at the University of Agricultural Sciences Vienna in 1901 and became a professor there five years later. Since 1900, E.T.S contributed to the commemoration and celebration of Mendel’s personality and work, including the re-publication of Mendel’s paper in 1901.


E.T.S. self-identified and is now identified as a rediscoverer of Mendel’s laws in the annus mirabilis 1900 along with Hugo de Vries and Carl Correns. However, during the second half of the 20th century, scholars argued that E.T. S misunderstood Mendel’s conceptual and terminological terms in his 1900 paper and excluded E.T.S from the list of rediscoverers. It was not until the summer of 2009, when a personal collection of E.T.S. held by the Archives of the Austrian Academy of Sciences in Vienna was catalogued and opened for historical research, that E.T. S’s 1898-1951 correspondences with Armin von Tschermak-Seysenegg, E.T. S’s older brother and a prominent physiologist, became available. The correspondences demonstrated that E.T.S. had a deep understanding of laws of heredity, and scholars now have argued for recovering E.T. S’s position as one of the rediscoverers.

William Bateson(1861-1926)

William Bateson (August 8, 1861 — February 8, 1926) was a British biologist who founded and named the science of genetics and whose experiments provided evidence basic to the modern understanding of heredity. Bateson gained his B.A. and M.A from the University of Cambridge in 1886, and became a professor of biology there in 1908. He left this chair in 1910 to spend the rest of his life directing the John Innes Horticultural Institution at Merton, South London (later moved to Norwich), and transformed it into a center for genetic research.

Bateson is now best known as the great companion to Mendel’s laws of heredity. Prior to the rediscovery of Mendel’s paper in 1900, Bateson focused on explaining evolution and published Materials for the Study of Variation in 1894, showing how some biological characteristics could appear or disappear abruptly in the progeny.


After 1900, Bateson contributed to promoting Mendel’s laws of heredity and publicized the usefulness of Mendelian science for practical breeders. In addition, Bateson first suggested using the word "genetics" (from the Greek gennō, γεννώ; "to give birth") to describe the study of inheritance and the science of variation in a personal letter to Adam Sedgwick (1854–1913, zoologist at Cambridge) on 18 April 1905, and used the term "genetics" publicly at the Third International Conference on Plant Hybridization in London in 1906, three years before Wilhelm Johannsen (1857 –1927) applied the word "gene" to the units of hereditary information.

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Walter Stanborough Sutton(1877-1916)

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Walter Stanborough Sutton (5 April 1877–10 November 1916) was an American geneticist and physician. Sutton was born in Utica, New York, the fifth of seven sons. When he was 10 years old, the family moved to Kansas. In 1896, he enrolled at the University of Kansas in engineering, and later in biological sciences, gaining a bachelor’s degree in 1900 and a master’s degree in 1901, as the first graduate student of Clarence Erwin McClung (1870-1946, American zoologist).


On McClung’s advice, Sutton transferred to the University of Columbia and studied with Edmund Beecher Wilson (1856-1939, American zoologist and geneticist), receiving his M.D. in 1907, and later accepted an appointment as Assistant Professor of Surgery at the University of Kansas. As a renowned surgeon, Sutton served in the army medical corpses in France during World War I in 1915. After returning to the U.S., Sutton died young at 39 for a ruptured appendix; ironically a subject he had studied and written on.


Sutton was best remembered for recognizing that chromosomes carry genetic material and serve as the basis for Mendelian inheritance. He published two seminal papers in the journal Biological Bulletin: ‘On the Morphology of the Chromosome Group in Brachystola magna’ in 1902, and ‘The Chromosomes in Heredity’ in 1903, which established the cytological basis of heredity. In addition to genetic studies, as a renowned surgeon, Sutton also worked on rectal administration of ether for anesthesia.

Theodor Boveri(1862-1915)

Theodor Heinrich Boveri (12 October 1862 – 15 October 1915) was a German zoologist, comparative anatomist, and co-founder of modern cytology. In 1881, Boveri entered the University of Munich and received the doctorate summa cum laude in 1885, with a thesis titled “Beiträge zur Kenntnis der Nervenfasern (Contributions to the knowledge of nerve fibers),” supervised by the anatomist Carl von Kupffer (1829-1902). He then worked for the Institute of Zoology at the University of Munich and in 1887 qualified as a university lecturer in zoology and comparative anatomy.


In 1893, Boveri became the director of the Zoological–Zootomical Institute at the University of Würzburg, where he stayed until he died in 1915 except for paying several occasional visits to the Zoological Station at Naples. Boveri married Marcella O'Grady (1863–1950) in Boston in 1897. Mrs Boveri actively participated in Boveri’s scientific work and the couple had one daughter, Margaret, in 1900.


Boveri contributed significantly to the chromosomal theory of heredity. In the early years Boveri experimented on the nematode Ascaris megalocephala (Parascaris equorum) that parasitizes the guts of horses and has only four chromosomes. In the influential 1889 paper titled “A sexually conceived organism without maternal traits,” Boveri reported his results and suggested that the chromosome content determines the characteristic traits of the organism.

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In 1901 and 1902, Boveri and his wife made observations on a specific species of sea urchin, Paracentrotus lividus. Boveri noticed a mismatch between the number of chromosomes in double-fertilized urchin eggs that develop immediately into four-cell embryos, skipping the usual two-cell stage. And he summarized in his 1902 paper “Über mehrpolige Mitosen als Mittel zur Analyse des Zellkerns [Concerning multipolar mitoses as a means of analyzing the cell nucleus]” that a balanced number of chromosomes is crucial for the development of organisms, and that cancer might relate to chromosomal abnormalities.

Wilhelm Ludvig Johannsen(1857 -1927)

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Wilhelm Johannsen (3 February 1857 – 11 November 1927) was a Danish pharmacist, botanist, plant physiologist, and geneticist. Johannsen started in the best primary and secondary schools of Copenhagen. Because his father could only afford one son at the university, Johannsen took vocational training as a pharmacist, which included a 1-year study at the University of Copenhagen where he became a favorite student of Eugenius Warming (1841-1924), the professor of botany. After passing the exams as a pharmacist, in 1881 Johannsen was appointed assistant at the Carlsberg Laboratory and pursued advanced biological studies including extended periods in Germany and France. Johannsen became a lecturer in plant physiology at the Royal Veterinary and Agricultural College in 1892, and in 1905 a professor ordinarius in plant physiology at the University of Copenhagen, where he spent the rest of his career. Johannsen enjoyed international fame and became a corresponding member of the Academy of Natural Sciences of Philadelphia since 1915.


Johannsen develops his genotype theory with a process: In 1895 he collaborated with Eugenius Warming on the third edition of the textbook Den almindelige Botanik (general botany) and contributed to combining cell theory with plant physiology. By studying plants, Johannsen became interested in the relationship between heredity and variation, and criticized Darwinism for taking selection, whether natural or artificial, as the main cause of hereditary change. In his 1903 monograph, Johannsen recorded the classical selection experiment on beans (Phaseolus vulgaris), a self-fertilizer which he termed as “pure line,” for studying the variability in the progeny.

Johannsen is best remembered for coining gene, genotype, and phenotype in his Germanic book Elements of the exact theory of heredity [Elemente der Exakten Erblichkeitslehere] (1909), and English paper “The Genotype Conception of Heredity” (1911). Finally, in Elemente Johannsen proposed that the relation between hereditary factors and characters was many-to-many. In this way, Johannsen took a holistic view of genotype and phenotype; differing from the modern interpretation, Johannsen took genotype, instead of gene, as the basic concept.

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