Mendel, Gregor Johann


Gregor Mendel (1822–1884) was a Moravian biologist from whose quantitative plant breeding studies were derived laws of inheritance that founded a new branch of biology, genetics. He crossed varieties of peas and examined the distribution of characters among offspring over successive generations. Hybrids resulting from crossing two varieties with contrasting characters did not breed true. They were not the ‘constant hybrids’ much sought by professional breeders that might lead to independent species. In the 1880s Mendel's work was appreciated by Wilhelm Focke and George Romanes, who initiated similar studies with animals. Studies with plants were initiated in the 1890s by European botanists who discovered Mendel's work in 1900. A relationship of hereditary units that determined characters – now known as genes – to chromosomes was noted by cytologist Michael Guyer in 1900. The major early advocate of Mendel's work, zoologist William Bateson, agreed with Mendel that new species could emerge discontinuously.

Key Concepts

  • For his experiments it was essential that Mendel chose characters in pea plants that would breed true.
  • He found that hybrids between lines which themselves bred true, did not breed true. They were not ‘constant hybrids’.
  • At that time many thought that constant hybrids would indicate a continuous species origination process.
  • From ‘brother‐sister’ matings of pea hybrids, Mendel derived quantitative laws.
  • His units that determined characters – now known as genes – were located to chromosomes by Michael Guyer.
  • Without knowledge of Mendel's laws, European botanists rediscovered them in plants.
  • William Bateson confirmed that Mendel's laws applied to various animal and plant species.
  • Mendel's laws were challenged by mathematical biologists (biometricians).
  • Mendel followed the statistics of his time and his results have withstood the test of time.
  • Mendel's view that new species can arise discontinuously without the involvement of natural selection has gained support.

Keywords: heredity; constant hybrids; Mendel's laws; genetics; chromosomes; speciation; Carl von Nägeli; George Romanes; Michael Guyer; William Bateson

Figure 1. Mendel, Gregor Johann. Courtesy of the National Library of Medicine, USA.
Figure 2. Pure lines breed true. Mendel sought pure lines (varieties) of peas. The units (elements) that represent contrasting pea characters are here symbolised by black or white circles. Members of pure lines bred true when crossed among themselves (1: black pollen with black ova and 2: white pollen with white ova). On crossing, any pairs from the first generation (F1 hybrids) should produce a second generation (F2 hybrids), all members of which would retain the parental character. The black line never produced a white. The white line never produced a black. Mendel was then prepared to study a cross between the lines (3).
Figure 3. Theoretical outcomes of crosses between different lines (symbolised as black or white). Mendel sought pure lines that when crossed displayed nonblending inheritance among child plants. Only one of the alternative parental characters would be displayed in a hybrid offspring (1–3). However, professional breeders were more interested in blending inheritance (here symbolised as grey; 4). In this case new characters such as a better flower colour in plants, or better wool in sheep, might emerge. When all hybrids displayed the black character (1), then black was deemed ‘dominant’ and white ‘recessive’. Conversely, when all hybrids displayed the white character (2), then white was dominant and black recessive. If a mixture resulted (3), there was neither dominance nor recessiveness.
Figure 4. Mendel's discovery of the 3:1 ratio when one character is dominant. In the F1 generation all hybrids appear identical (1). This equals the first case in Figure, with black symbolising the dominant character. The crossing of any pairs selected randomly from the F1 generation produced an F2 generation with a minority of recessives (white) in the ratio (black:white = 3:1). Here, the three black forms appear equal. With blending inheritance (2), which Mendel did not study, there would be visible variation among the three nonwhite forms (explained in Figure).
Figure 5. Mendel's recognition that his chosen parental characters (here symbolised as black or white) existed in dual forms in each parent. These forms were separated when pollen and ova were formed (gametogenesis). In the F1 generation all hybrids are equal (black and white are both represented), but as black is dominant, they all appear black. The crossing of any pairs from the F1 generation will result, statistically, in an F2 generation with, for each one white, one pure black and two with black and white, both represented but appearing black. Applying the same interpretation with the blending model shown in Figure, these two would appear grey and, if crossed with each other, would not breed true.
Figure 6. Statue of Mendel as erected in 1910 (a) and as it is today (b). Courtesy of the Mendelianum, Moravian Museum, Brno.


Abbott S and Fairbanks DJ (2016) Experiments on plant hybrids by Gregor Mendel. Genetics 204: 407–422.

Baumgartner A and von Ettinghausen A (1842) Die Naturlehre nach ihrem gegenwärtigen Zustand mit Rücksicht auf mathematische Begründung. Wien: Carl Gerold.

Bungener P and Buscaglia M (2003) Early connection between cytology and Mendelism. Michael F. Guyer's contribution. History and Philosophy of the Life Sciences 25: 27–50.

Cock AG and Forsdyke DR (2008) Treasure Your Exceptions. In: The Science and Life of William Bateson. New York: Springer.

Fairbanks DJ and Abbott S (2016) Darwin's influence on Mendel: evidence from a new translation of Mendel's paper. Genetics 204: 401–405.

Fisher RA (1936) Has Mendel's work been rediscovered? Annals of Science 1: 115–137.

Focke WO (1881) Die Pflanzen‐Mischlinge. Ein Beitrag zur Biologie der Gewächse. Borntaeger: Berlin.

Forsdyke DR (2010) George Romanes, William Bateson, and Darwin's “weak point”. Notes and Records of the Royal Society 64: 139–154.

Forsdyke DR (2017) Speciation: Goldschmidt's chromosomal heresy, once supported by Gould and Dawkins, is again reinstated. Biological Theory 12: 4–12.

Guyer MF (1900) Spermatogenesis in hybrid pigeons. Science 11: 248–249, 312.

Iltis H (1932) Life of Mendel, 1st edn. London: Allen and Unwin.

Iltis A (1954) Gregor Mendel's autobiography. Journal of Heredity 45: 231–234.

Klein J and Klein N (2013) Solitude of a Humble Genius – Gregor Johann Mendel, vol. 1. Heidelberg: Springer.

Meijer OG (1982) The essence of Mendel's discovery. In: Orel V (ed) Gregor Mendel and the Foundation of Genetics, the Past, and Present of Genetics, pp. 173–200. Brno: The Mendelianum of the Moravian Museum.

Mendel GJ (1866) Experiments on plant hybridization. Verhandlungen des naturforschenden Vereines in Brünn 4: 3–47.

Mendel GJ (1870) On Hieracium hybrids obtained by artificial fertilization. Verhandlungen des naturforschenden Vereines in Brünn 8: 26–31.

Nivet C (2004) Une maladie énigmatique dans la vie de Gregor Mendel. Médicine Sciences 20: 1050–1053.

Nivet C (2005) 1848: Gregor Mendel, le moine qui voulait être citoyen. Médicine Sciences 22: 430–433.

Nogler GA (2006) The lesser‐known Mendel: his experiments on Hieracium. Genetics 172: 1–6.

Olby R and Gautrey P (1968) Eleven references to Mendel before 1900. Annals of Science 24: 7–20.

Olby R (1985) The Origins of Mendelism, 2nd edn. Chicago, IL: Chicago University Press.

Orel V and Verbig A (1984) Mendel's involvement in the plea for freedom on teaching in the revolutionary year of 1848. Folia Mendeliana 19: 223–233.

Orel V (1996) Gregor Mendel, the First Geneticist. Oxford, UK: Oxford University Press.

Orel V (2000) Constant hybrids in Mendel's research. History and Philosophy of the Life Sciences 22: 291–299.

Romanes GJ (1881) Hybridism. In: Encyclopaedia Britannica, 9th edn. .Edinburgh, Scotland: A & C Black.

Romanes GJ (1893) Letter to Thiselton‐Dyer, 15th Sept. In: Romanes E (ed) The Life and Letters of George John Romanes, pp. 314–315. London: Longman, Green, and Co.

Romanes GJ (1894) Letter to Schafer, 18th May. London: Wellcome Museum of the History of Medicine.

Schwartz JS (2011) Darwin's Disciple. George John Romanes. A Life in Letters. Philadelphia, PA: American Philosophical Society.

Further Reading

Bateson W (1909) Mendel's Principles of Heredity. Cambridge, UK: Cambridge University Press.

Blumberg RB (2010) MendelWeb.

Forsdyke DR (2012) Blending Inheritance (12 short You Tube videos).

Forsdyke DR (2016) Evolutionary Bioinformatics, 3rd edn. New York: Springer.

Forsdyke DR (2017a) Hybridism and the Germ‐Cell.∼forsdyke/guyer.htm

Forsdyke DR (2017b) William Bateson: Two Levels of Genetic Information.∼forsdyke/bateson1.htm

Lock RH (1916) Recent Progress in the Study of Variation, Heredity, and Evolution, 4th edn. London: John Murray.

Roberts HF (1929) Plant Hybridization before Mendel. Princeton, NJ: Princeton University Press.

Romanes GJ (1897) Darwin, and After Darwin. Vol III. Isolation and Physiological Selection. London: Longmans, Green, and Co.

de Vries H (1910) Intracellular Pangenesis, translated from 1889 German edition by CS Gager. Chicago, IL: Open Court Publishing Co.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Forsdyke, Donald R(Apr 2018) Mendel, Gregor Johann. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002544.pub2]