Mendel worked with seven characteristics ofpea plants: plant height, pod shape and color, seed shape and color, and flower position and color. Taking seed color as an example, Mendel showed that when a true-breeding yellow pea and a true-breeding green pea were cross-bred, their offspring always produced yellow seeds. However, in the next generation, the green peas reappeared at a ratio of 1 green to 3 yellow. To explain this phenomenon, Mendel coined the terms "recessive" and "dominant" in reference to certain traits. In the preceding example, the green trait, which seems to have vanished in the first filial generation, is recessive, and the yellow is dominant. He published his work in 1866, demonstrating the actions of invisible "factors"—now calledgenes—in predictably determining the traits of an organism. The actual genes were only discovered in a long process that ended in 2025 when the last three of the seven Mendel genes were identified in the peagenome.[9]
The profound significance of Mendel's work was not recognized until the turn of the 20th century (more than three decades later) with the rediscovery of his laws.Erich von Tschermak,Hugo de Vries andCarl Correns independently verified several of Mendel's experimental findings in 1900, ushering in the modern age of genetics.[10][11]
Early life and education
Mendel was born into aGerman-speaking family inHeinzendorf bei Odrau,[2] inSilesia,Austrian Empire (now Hynčice in theCzech Republic).[7] He was the son of Anton and Rosine (Schwirtlich) Mendel and had one older sister, Veronika, and one younger, Theresia. They lived and worked on a farm which had been owned by the Mendel family for at least 130 years[12] (the house where Mendel was born is now a museum devoted to Mendel).[13] During his childhood, Mendel worked as a gardener and studiedbeekeeping. As a young man, he attendedgymnasium inTroppau (Czech:Opava). Due to illness, he had to take four months off during his gymnasium studies.[14] From 1840 to 1843, he studied practical and theoretical philosophy and physics at the Philosophical Institute of theUniversity of Olomouc (German:Olmütz), taking another year off because of illness. He also struggled financially to pay for his studies, and Theresia gave him her dowry. Later he helped support her three sons, two of whom became doctors.[15]
He became a monk partly because it enabled him to obtain an education without paying for it himself.[16] As the son of a struggling farmer, the monastic life, in his words, spared him the "perpetual anxiety about a means of livelihood."[17] Born Johann Mendel, he was given the name "Gregor" (Řehoř in Czech)[2] when he joined theOrder of Saint Augustine.[18]
Academic career
Mendel (seated second from right and numbered "2") with other faculty at the Brno Realschule in 1864 (Alexander Zawadzki is labelled "1".)
When Mendel entered the Faculty of Philosophy, the Department of Natural History and Agriculture was headed byJohann Karl Nestler, who conducted extensive research on hereditary traits of plants and animals, especially sheep. Upon recommendation of hisphysics teacherFriedrich Franz,[19] Mendel entered theAugustinianSt Thomas's Abbey inBrno and began his training as aCatholic priest. Mendel worked as a substitute high school teacher. In 1850, he failed his exams' oral part, the last of three parts, to become a certified high school teacher. In 1851, he was sent to theUniversity of Vienna to study under the sponsorship ofAbbotCyril František Napp so that he could get a more formal education.[18] At Vienna, his professor of physics wasChristian Doppler.[20] Mendel returned to his abbey in 1853 as a teacher, principally of physics. In 1854 he metAleksander Zawadzki who encouraged his research in Brno. In 1856, he took the exam to become a certified teacher and again failed the oral part.[21] In the summer of 1862, he joined an organised group tour to Paris andLondon, where he visited theInternational Exhibition and major scientific sites, a trip that may have influenced the final stage of his hybridisation research.[22] In 1867, he succeeded Napp as abbot of the monastery.[23]
After he was elevated as abbot in 1868, his scientific work largely ended, as Mendel became overburdened with administrative responsibilities, especially a dispute with the civil government over its attempt to impose special taxes on religious institutions.[24] Mendel died on 6 January 1884, at the age of 61, in Brno,[2] from chronicnephritis. Czech composerLeoš Janáček played the organ at his funeral.[25] After his death, the succeeding abbot burned all papers in Mendel's collection, to mark an end to the disputes over taxation.[26] Theexhumation of Mendel's corpse in 2021 delivered somephysiognomic details like body height (168 cm (66 in)). Hisgenome was analysed, revealing that Mendel was predisposed to heart problems.[27]
Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation.
Mendel, known as the "father of modern genetics," chose to study variation in plants in his monastery's 2 hectares (4.9 acres) experimental garden.[28] Mendel was assisted in his experimental design by Aleksander Zawadzki while his superior abbotNapp wrote to discourage him, saying that the Bishop giggled when informed of the detailed genealogies of peas.[29]
After initial experiments with pea plants, Mendel settled on studying seven traits that seemed to be inherited independently of other traits: seed shape, flower color, seed coat tint, pod shape, unripe pod color, flower location, and plant height. He first focused on seed shape, which was either angular or round.[30] Between 1856 and 1863 Mendel cultivated and tested some 28,000 plants, the majority of which werepea plants (Pisum sativum).[31][32][33] This study 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 hadpurebredrecessivetraits, two out of four werehybrids, and one out of four were purebreddominant. His experiments led him to make two generalizations, theLaw of Segregation and theLaw of Independent Assortment, which later came to be known as Mendel's Laws of Inheritance.[34]
Initial reception of Mendel's work
Mendel presented his paper,Versuche über Pflanzenhybriden ("Experiments on Plant Hybridization"), at two meetings of the Natural History Society of Brno inMoravia on 8 February and 8 March 1865.[35] It generated a few favorable reports in local newspapers,[33] but was ignored by the scientific community. When Mendel's paper was published in 1866 inVerhandlungen des naturforschenden Vereines in Brünn,[36] it was seen as essentially about hybridization rather than inheritance, had little impact, and was cited only about three times over the next thirty-five years. His paper was criticized then but is now considered a seminal work.[37] Notably,Charles Darwin was not aware of Mendel's paper, and it is envisaged that if he had been aware of it, genetics as it exists now might have taken hold much earlier.[38][39] Mendel's scientific biography thus provides an example of the failure of obscure, highly original innovators to receive the attention they deserve.[40]
Rediscovery of Mendel's work
About forty scientists listened to Mendel's two groundbreaking lectures, but it would appear that they failed to understand the implications of his work. Later, he also carried on a correspondence withCarl Nägeli, one of the leading biologists of the time, but Nägeli also failed to appreciate Mendel's discoveries. At times, Mendel must have entertained doubts about his work, but not always: "My time will come," he reportedly told a friend,[17] Gustav von Niessl.[41]
During Mendel's lifetime, most biologists held the idea that all characteristics were passed to the next generation throughblending inheritance (indeed, many effectively are), in which the traits from each parent are averaged.[42][43] Instances of this phenomenon are now explained by the action of multiple genes withquantitative effects. Charles Darwin tried unsuccessfully to explain inheritance through a theory ofpangenesis. It was not until the early 20th century that the importance of Mendel's ideas was realized.[33]
By 1900, research aimed at finding a successful theory of discontinuous inheritance rather thanblending inheritance led to independent duplication of his work byHugo de Vries andCarl Correns and the rediscovery of Mendel's writings and laws. Both acknowledged Mendel's priority, and it is thought probable that de Vries did not understand the results he had found until after reading Mendel.[33] ThoughErich von Tschermak was originally also credited with rediscovery, this is no longer accepted because he did not understandMendel's laws.[44] Though de Vries later lost interest in Mendelism, other biologists started to establish modern genetics as a science. All three of these researchers, each from a different country, published their rediscovery of Mendel's work within a two-month span in the spring of 1900.[45]
Mendel's results were quickly replicated, and genetic linkage quickly worked out. Biologists flocked to the theory; even though it was not yet applicable to many phenomena, it sought to give agenotypic understanding of heredity, which they felt was lacking in previous studies of heredity, which had focused onphenotypic approaches.[46] Most prominent of these previous approaches was thebiometric school ofKarl Pearson andW. F. R. Weldon, which was based heavily on statistical studies of phenotype variation. The strongest opposition to this school came fromWilliam Bateson, who perhaps did the most in the early days of publicising the benefits of Mendel's theory (the word "genetics", and much of the discipline's other terminology, originated with Bateson). This debate between the biometricians and the Mendelians was extremely vigorous in the first two decades of the 20th century, with the biometricians claiming statistical and mathematical rigor,[47] whereas the Mendelians claimed a better understanding of biology.[48][49] Modern genetics shows that Mendelian heredity is, in fact, an inherently biological process, though not all genes of Mendel's experiments are yet understood.[50][51]
In theSoviet Union and China, Mendelian genetics was rejected in favor ofLamarckism, leading to imprisonment and even execution of Mendelian geneticists (seeLysenkoism).
Modern analysis of the genes causing Mendel's pea phenotypes
Mendel postulated that seven "factors" determine the features he studied in peas. These factors are called "genes" today, but the nature of these genes remained mysterious for more than a century. The effort to identify these genes lasted until 2025 when the last 3 genes were discovered.[9] The seven genes are as follows (genes are abbreviated PsXYZ forPisum sativum, the scientific name of the pea): thewrinkled phenotype of peas (wild-type round) is caused by aninsertion in thePsSBE1 gene. Theyellow phenotype (wild-type: green) is caused by an insertion or mutation in thePsSGR gene. Thewhite phenotype of the flower color (wild-type:purple) is caused by adeletion in thePsbHLH gene. Thedwarf phenotype is caused by thePsGA3ox1 gene while the pod color phenotype (yellow vs.green) is caused by thePsChlG gene. Finally, the pod shape is determined by thePsCLE41 gene which causes theconstricted orinflated phenotypes and thePsCIK2/3 gene causes theterminal andaxial flower position.[9]
Other experiments
Mendel also experimented withhawkweed (Hieracium).[54] He published a report on his work with hawkweed,[55] a group of plants of great interest to scientists at the time because of their diversity. However, the results of Mendel's inheritance study in hawkweeds were unlike those for peas; the first generation was very variable, and many of their offspring were identical to the maternal parent. In his correspondence withCarl Nägeli he discussed his results but was unable to explain them.[54] It was not appreciated until the end of the nineteenth century that many hawkweed species wereapomictic, producing most of their seeds through an asexual process.[41][56]
Mendel appears to have kept animals at the monastery, breeding bees in custom-designedbee hives.[57][58] None of his results on bees survived, except for a passing mention in the reports of the Moravian Apiculture Society.[59] All that is known definitely is that he used Cyprian and Carniolan bees,[60] which were particularly aggressive, to the annoyance of other monks and visitors of the monastery, such that he was asked to get rid of them.[61] Mendel, on the other hand, was fond of his bees and referred to them as "my dearest little animals".[62]
After his death, Mendel's colleagues remembered that he bred mice, crossing varieties of different size, although Mendel has left no record of any such work. A persistent myth has developed that Mendel turned his attention to plants only after Napp declared it unseemly for a celibate priest to closely observe rodent sex. In a 2022 biography, Daniel Fairbanks argued that Napp could hardly have given such a pronouncement, as Napp personally oversaw sheep breeding on the monastery's extensive agricultural estate.[63]
Mendel also studiedastronomy andmeteorology,[23] founding the 'Austrian Meteorological Society' in 1865.[20] The majority of his published works were related to meteorology.[20]
In 1936,Ronald Fisher, a prominent statistician and population geneticist, reconstructed Mendel's experiments, analyzed results from the F2 (second filial) generation, and found the ratio of dominant to recessive phenotypes (e.g., yellow versus green peas; round versus wrinkled peas) to be implausibly and consistently too close to the expected ratio of 3 to 1.[65][66][67] Fisher asserted that "the data of most, if not all, of the experiments have been falsified to agree closely with Mendel's expectations".[65] Mendel's alleged observations, according to Fisher, were "abominable," "shocking,"[68] and "cooked."[69]
Other scholars agree with Fisher that Mendel's various observations come uncomfortably close to Mendel's expectations.A. W. F. Edwards,[70] for instance, remarks: "One can applaud the lucky gambler; but when he is lucky again tomorrow, and the next day, and the following day, one is entitled to become a little suspicious". Three other lines of evidence likewise lend support to the assertion that Mendel's results are indeed too good to be true.[71]
Fisher's analysis gave rise to theMendelian paradox: Mendel's reported data are, statistically speaking, too good to be true, yet "everything we know about Mendel suggests that he was unlikely to engage in either deliberate fraud or in an unconscious adjustment of his observations".[71] Several writers have attempted to resolve this paradox.
One attempted explanation invokesconfirmation bias.[72] Fisher accused Mendel's experiments as "biased strongly in the direction of agreement with expectation[...] to give the theory the benefit of the doubt".[65] In a 2004 article, J.W. Porteous concluded that Mendel's observations were indeed implausible.[73] An explanation for Mendel's results based ontetrad pollen has been proposed, but reproduction of the experiments showed no evidence that the tetrad-pollen model explains any of the bias.[74]
Another attempt[71] to resolve the Mendelian paradox notes that a conflict may sometimes arise between the moral imperative of a bias-free recounting of one's factual observations and the even more important imperative of advancing scientific knowledge. Mendel might have felt compelled "to simplify his data to meet real, or feared editorial objections."[70] Such an action could be justified on moral grounds (and hence provide a resolution to the Mendelian paradox) since the alternative—refusing to comply—might have hindered the growth of scientific knowledge. Similarly, like so many other obscure innovators of science,[40] Mendel, a little-known innovator of working-class background, had to "break through the cognitive paradigms and social prejudices" of his audience.[70] If such a breakthrough "could be best achieved by deliberately omitting some observations from his report and adjusting others to make them more palatable to his audience, such actions could be justified on moral grounds."[71]
Daniel L. Hartl andDaniel J. Fairbanks reject outright Fisher's statistical argument, suggesting that Fisher incorrectly interpreted Mendel's experiments. They find it likely that Mendel scored more than ten progeny and that the results matched the expectation. They conclude: "Fisher's allegation of deliberate falsification can finally be put to rest, because on closer analysis it has proved to be unsupported by convincing evidence".[68][75] In 2008 Hartl and Fairbanks (with Allan Franklin and AWF Edwards) wrote a comprehensive book in which they concluded that there were no reasons to assert Mendel fabricated his results, nor that Fisher deliberately tried to diminish Mendel's legacy.[76] Reassessment of Fisher's statistical analysis, according to these authors, also disproves the notion of confirmation bias in Mendel's results.[77][78]
^Gregor Mendel, Alain F. Corcos, Floyd V. Monaghan, Maria C. Weber "Gregor Mendel's Experiments on Plant Hybrids: A Guided Study", Rutgers University Press, 1993.
^Eckert-Wagner, Silvia (2004).Mendel und seine Erben: Eine Spurensuche [Mendel and His Heirs: A search for traces] (in German). Norderstedt: Books on Demand. p. 113.ISBN978-3-8334-1706-1.
^Van Dijk, Peter J. (2020). "Mendel's journey to Paris and London: context and significance for the origin of genetics".History and Philosophy of the Life Sciences. 56(1-2):5–47.
^Mendel, J.G. (1866). "Versuche über Pflanzenhybriden",Verhandlungen des naturforschenden Vereines in Brünn, Bd. IV für das Jahr, 1865,Abhandlungen: 3–47. For the English translation, see:Druery, C.T.; Bateson, William (1901)."Experiments in plant hybridization"(PDF).Journal of the Royal Horticultural Society.26:1–32.Archived(PDF) from the original on 2 September 2000. Retrieved9 October 2009.
^Lorenzano, P (2011). "What would have happened if Darwin had known Mendel (or Mendel's work)?".History and Philosophy of the Life Sciences.33 (1):3–49.PMID21789954.
^Liu, Y (2005). "Darwin and Mendel: who was the pioneer of genetics?".Rivista di Biologia.98 (2):305–22.PMID16180199.
^Pilpel, Avital (September 2007). "Statistics is not enough: revisiting Ronald A. Fisher's critique (1936) of Mendel's experimental results (1866)".Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences.38 (3):618–26.doi:10.1016/j.shpsc.2007.06.009.PMID17893069.
^Hall, Brian Keith; Hallgrímsson, Benedikt; Strickberger, Monroe W. (2014).Strickberger's evolution (5 ed.). Burlington, Mass.: Jones & Bartlett Learning. pp. 10–11.ISBN978-1-4496-1484-3.
^Mendel, Gregor (1869). "Ueber einige aus künstlicher Befruchtung gewonnenen Hieracium-Bastarde. (On Hieracium hybrids obtained by artificial fertilisation)".Verh. Naturf. Ver. Brünn. 8 (Abhandlungen):26–31.
^Matalova, A; Kabelka, A (1982)."The beehouse of Gregor Mendel".Casopis Moravskeho Musea. Acta Musei Moraviae – Vedy Prirodni. Car Morav Mus Acta Mus Vedy Prir.57:207–12.
Hugo Iltis,Gregor Johann Mendel. Leben, Werk und Wirkung. Berlin: J. Springer. 426 pages. (1924)
Translated byEden andCedar Paul asLife of Mendel. New York: W. W. Norton & Co, 1932. 336 pages. New York: Hafner, 1966: London: George Allen & Unwin, 1966. Ann Arbor: University Microfilms International, 1976.
Translated by Zhenyao Tan asMên-tê-êrh chuan. Shanghai: Shang wu yin shu guan, 1924. 2 vols. in 1, 661 pp. Shanghai: Shang wu yin shu guan, Minguo 25 [1936].
Translated asZasshu shokubutsu no kenkyū. Tsuketari Menderu shōden. Tōkyō: Iwanami Shoten, Shōwa 3 [1928]. 100 pp. Translated by Yuzuru Nagashima asMenderu no shōgai. Tōkyō: Sōgensha, Shōwa 17 [1942].Menderu den. Tōkyō: Tōkyō Sōgensha, 1960.
Klein, Jan; Klein, Norman (2013).Solitude of a Humble Genius – Gregor Johann Mendel: Volume 1. Heidelberg: Springer.ISBN978-3-642-35253-9.
Robert Lock,Recent Progress in the Study of Variation, Heredity and Evolution, London, 1906
Orel, Vítĕzslav (1996).Gregor Mendel: the first geneticist. Oxford [Oxfordshire]: Oxford University Press.ISBN978-0-19-854774-7.
Curt Stern and Sherwood ER (1966)The Origin of Genetics.
Taylor, Monica (July–September 1922)."Abbot Mendel".Dublin Review. London: W. Spooner.
Tudge, Colin (2000).In Mendel's footnotes: an introduction to the science and technologies of genes and genetics from the nineteenth century to the twenty-second. London: Vintage.ISBN978-0-09-928875-6.
