Anthropology Gregor Mendel
by
Anne Buchanan, Kenneth Weiss
  • LAST MODIFIED: 25 June 2013
  • DOI: 10.1093/obo/9780199766567-0092

Introduction

Gregor Mendel (b. 1822–d. 1884) was an Augustinian friar from what is now the Czech Republic. He became known posthumously as the Father of Modern Genetics because of his work documenting the inheritance of selected traits in garden peas. Mendel spent eight years experimenting with crosses of pea plants that differed by single traits such as height, texture, and color of the pea or color of the blossom. He concluded, after cataloguing nearly thirty thousand peas, that traits do not blend; that traits in the first generation offspring of crosses between plants will all be the same because some traits are dominant and some are recessive (terms that he introduced), and the recessive trait will not be expressed in the first generation; and that traits will segregate in subsequent generations by expected ratios. He further concluded that there must be elements responsible for all traits; that every individual has two distinct elements for each trait, one inherited from each parent, and the two elements for a given trait segregate in the sense that only one is transmitted to each offspring; and that the elements for different traits are transmitted independently to each offspring. Mendel’s work was published in 1866 but did not become widely known until 1900, when it was finally recognized as a seminal contribution to the understanding of inheritance. Scholars have long debated a number of aspects of his work, including what motivated him, what he thought he had discovered, whether it is correct to attribute what we now know as Mendel’s Laws of Inheritance in fact to Mendel, what he knew and believed about Charles Darwin’s theory of evolution, whether his results might be too good to be true, and thus whether he might have altered his data to make his point. It has been suggested over the years that Charles Darwin had a copy of Mendel’s paper in his library that he never read, but most Darwin scholars disregard this story as folklore and believe that it is likely that Darwin never knew of Mendel’s work. As for Mendel’s lasting legacy, modern genetics has recognized that his view of inheritance was revolutionary for its time but in light of current knowledge, we now know that it has fundamental limitations.

Bibliographies

There are a number of online resources for works on Mendel, which vary in completeness and the extent to which they are maintained and up-to-date. The most thorough of these is MendelWeb, which includes an extensive bibliography of books and journal articles, and selected chapters from numerous biographies as well as Mendel’s papers in English and German and in a variety of formats. This site was created as a teaching resource, and, while extensive, it remains a work in progress. Vítĕzslav Orel, renowned Mendel scholar, started and long edited a collection of papers on Mendel and his work, Folia Mendeliana (Jakubíček 1966). The periodical is published by the Moravian Museum.

Biographies

Relatively few biographies of Mendel have been published over the years, perhaps because most of his letters and papers were burned not long after his death, thus making it impossible to reconstruct many of the more interesting aspects of his life and work. Even so, some excellent biographies have been written. Mendel himself penned a short, rather poignant autobiography in 1850, at the age of twenty-eight, in which he describes his childhood on a farm and difficulty securing an education. This autobiography is reproduced in Iltis 1954. Hugo Iltis, a biologist and resident of Brno, wrote the first definitive biography, published in German as Iltis 1924 and in English translation as Iltis, et al. 1932. Orel 1996 is a detailed and thorough study that places Mendel’s work in historical context. Robin Marantz Henig has written perhaps the best-known modern biography, Henig 2000. Simon Mawer wrote a beautifully illustrated biography, Mawer 2006, to accompany a 2006 exhibit on Mendel for the Field Museum in Chicago. Sedwick and Gardener 2002 is an excellent thirty-minute film biography, Gregor Mendel: From the Garden to the Genome. Edelson 1999 includes a brief history of genetics for young adults.

  • Edelson, Edward. 1999. Gregor Mendel and the roots of genetics. New York: Oxford Univ. Press.

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    One of the Oxford Portraits in Science series about scientific figures, this work is a biography of Mendel written for young adults in grades nine to twelve.

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    • Henig, Robin Marantz. 2000. The monk in the garden: The lost and found genius of Gregor Mendel, the father of genetics. Boston: Houghton Mifflin.

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      A very nicely written modern biography of Mendel, in the style of historical fiction. Also see Life.

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      • Iltis, Anne. 1954. Gregor Mendel’s autobiography. Journal of Heredity 45.5: 231–234.

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        Mendel’s two-page autobiography, written in 1850. The publication was introduced by Anne Iltis, then curator of the Mendel Museum in Virginia, and includes a reproduction of his handwritten pages. Available online for purchase or by subscription. Also see Life.

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        • Iltis, Hugo. 1924. Gregor Johann Mendel. Leben, werk und wirkung. Berlin: Springer.

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          The first biography of Gregor Mendel, in German. Iltis, a native of Brno, was a biologist and a successor to Mendel as a teacher in Brno. In 1906 he served as secretary for Naturforschender Verein in Brno, the society that published Mendel’s papers in 1865, and was a biology professor in Brno from 1905 to 1938. For this biography, Iltis interviewed several associates of Mendel as well as former pupils. Also see Life.

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          • Iltis, Hugo. 1932. Life of Mendel. Translated by Eden Paul and Cedar Paul. New York: Norton.

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            English translation of the first Mendel biography. Also see Life.

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            • Mawer, Simon. 2006. Gregor Mendel: Planting the seeds of genetics. New York: Abrams.

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              A beautiful coffee-table book, written by a novelist as a companion to the 2006 Mendel exhibit developed by The Field Museum, Chicago. Also see Life, Mendel’s Laws, and Lingering Questions.

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              • Orel, Vítĕzslav. 1996. Gregor Mendel: The first geneticist. Translated by Stephen Finn. New York: Oxford Univ. Press.

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                English translation of the second biography written by a Brno resident and world-renowned Mendel scholar. Also see Life, Work, and Eugenics.

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                • Sedwick, J. Lee, and Larry Gardner. 2002. Gregor Mendel: From the garden to the genome. VHS. Greenville, NC: East Carolina University.

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                  This video is a fine introduction to the life and work of Mendel.

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                  Life

                  The facts of Mendel’s life are sparse, but what is known and described by Henig 2000, Mawer 2006, Orel 1996 and Iltis, et al. 1932 is that Mendel was born on 22 July 1822 in Heinzendorf, Austria, now Hynčice, Czech Republic, and was christened Johann. The only son of a peasant farmer and his wife, he had two sisters. His parents valued education and sent him to Gymnasium at Troppau at age twelve, where his promise was quickly recognized. He studied with a teacher interested in horticulture, graduated in 1840 and moved to Olmütz, where he attempted to make his living as a private teacher. In 1954 Anne Iltis reproduces Mendel’s brief autobiography, written in 1850 when he was just twenty-eight (see Iltis 1954) in which he writes that as the only son in a farming family he was expected to take over the farm, but he preferred to continue his studies. Because his family was so poor, his most viable alternative was to become a monk of the Augustinian Order, which he did in 1843, at age twenty-one. He joined the diocese of Brünn (Brno) on the recommendation of his physics teacher at school, where he was assigned the name Gregor. St Augustine’s was a scholarly order, and Mendel was encouraged by a forward-thinking abbot to continue his studies. In 1851 Mendel went to the University of Vienna and studied physics, mathematics, and astronomy, among other subjects, which facilitated his later statistical treatment of his plant breeding experiments. He returned to the abbey in 1853 where he resumed teaching and began his experiments with peas. Mendel became abbot of the convent in 1868, after which he had less time for his own work, although he did experiment with bees as well as other plants, which, to his disappointment, did not follow the same rules of inheritance as peas. Dunn 1965 describes Mendel’s further experiments and his subsequent disappointment. Mendel died in 1884, uncertain that his work on peas was as significant as he had hoped, although he is reported to have told others that its importance would eventually be recognized.

                  • Dunn, L. C. 1965. Mendel, his work and his place in history. Special issue: Commemoration of the publication of Gregor Mendel’s pioneer experiments in genetics. Proceedings of the American Philosophical Society 109.4: 189–198.

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                    Written on the centennial of the publication of Mendel’s paper on peas, this thoughtful article describes what is known about Mendel’s life, including his disappointment at not confirming his work with other plants, and considers Mendel’s place in history. Available online for purchase or by subscription. Also see Work.

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                    • Henig, Robin Marantz. 2000. The monk in the garden: The lost and found genius of Gregor Mendel, the father of genetics. Boston: Houghton Mifflin.

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                      Written as historical fiction, Henig fleshes out the facts known about Mendel’s life. Also see Biographies.

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                      • Iltis, Anne. 1954. Gregor Mendel’s autobiography. Journal of Heredity 45.5: 231–234.

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                        Mendel’s two-page autobiography, written in 1850 before he began his experiments. He describes his education and the circumstances that lead to his decision to join the Augustinian order. The publication is introduced by Anne Iltis, then curator of the Mendel Museum in Virginia, and includes the reproduction of his handwritten pages. Available online for purchase or by subscription. Also see Biographies.

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                        • Iltis, Hugo. 1924. Gregor Johann Mendel: Leben, werk und wirkung. Berlin: Springer.

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                          The first biography of Gregor Mendel, in German, written by a native of Brno, a biologist and teacher and a near contemporary of Mendel. Iltis became secretary for Naturforschender Verein in Brno in 1906, the society that published Mendel’s papers in 1865, and later a Mendel biographer, biology professor, and organizer of the Mendel Museum in Fredericksburg, Virginia. Also see Biographies.

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                          • Iltis, Hugo. 1932. Life of Mendel. Translated by Eden Paul and Cedar Paul. New York: Norton.

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                            An English translation the first Mendel biography, by Hugo Iltis. Iltis was a biologist and native of Brno and a near contemporary of Mendel. As such, and because he interviewed several of Mendel’s former associates and pupils, his biography has an irreproducible slant. Also see Biographies.

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                            • Mawer, Simon. 2006. Gregor Mendel: Planting the seeds of genetics. New York: Abrams.

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                              This book was written by a novelist as a companion to the 2006 Mendel exhibit developed by The Field Museum, Chicago. Mawer clearly loves his subject and writes with great enthusiasm and attention to detail. Also see Biographies, Mendel’s Laws, and Lingering Questions.

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                              • Orel, Vítĕzslav. 1996. Gregor Mendel: The first geneticist. Translated by Stephen Finn. New York: Oxford Univ. Press.

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                                One of a select few biographies written by Brno residents. Orel is a historian of science and well-known Mendel scholar. Also see Biographies, Work, and Eugenics.

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                                Work

                                In 1854 Mendel acquired thirty-four varieties of pea seed, Pisum sativum, from local nurseries and spent the next two years growing them to determine which characters bred true. Of these he chose seven traits to follow through multiple generations. He produced seven crosses, each repeated twice, from a seed plant with a particular trait and the second time with that same trait from the pollen plant. In this way he determined that the male and female contribute equally to the offspring. He carried on his experiments for eight years, counting the occurrence of these traits in nearly thirty thousand peas. Because he chose his traits well, he was able to document what became known as recessive and dominant inheritance, as well as the random segregation of alleles in offspring and the independent inheritance of genes for traits using a sample size large enough to produce robust results. Mendel described his findings in two lectures, which he gave to the Brünn Society for Natural Science in 1865. The lectures were subsequently published as Mendel 1866 and in English as Mendel 1901 in the Proceedings of the Natural History Society of Brünn, but his work met a muted reception and was long ignored. Some of his notation and terms he introduced are still widely used. He carefully chose his traits, knowing that some quantitative traits did not segregate in the same way as his selected qualitative (dichotomous state) traits. The work is described by Bateson 1902, Bateson and Saunder 1902 and its importance noted in Orel 1996 as well as in the Biographies. Among others, Mendel sent his paper to renowned Swiss botanist, Karl Wilhelm von Nägeli, for review but Nägeli seems not to have understood its importance and recommended that Mendel verify his findings with further experiments, this time on Hieracium, or hawkweed. Unfortunately, these are plants with unusual modes of inheritance, and the experiments did not give Mendel his expected results. Among the few documents written by Mendel that survived his death were the letters he wrote to Nägeli, compiled in Mendel 1950. He wrote a paper describing his work on hawkweed and then did no further work with plants. He had a lifelong interest in meteorology as well as horticulture and published a paper in 1871 suggesting the cause of tornadoes. His reasoning was largely correct, but this paper too was long ignored, as Dunn 1965 and Dubec and Orel 1980 write.

                                • Bateson, William. 1902. Mendel’s principles of heredity. A defence. London: Cambridge Univ. Press.

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                                  British geneticist William Bateson was an enthusiastic early promoter of Mendel’s work and the first translator and editor of his paper into English. Bateson writes that Mendel’s principles “will certainly play a conspicuous part in all future discussions of evolutionary problems” (p. 8). Also see the Debate Over the Lag in Recognition of Mendel’s Work.

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                                  • Bateson, William, and E. R. Saunders. 1902. The facts of heredity in the light of Mendel’s discovery. Reports to the Evolution Committee of the Royal Society of London 1:125–160.

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                                    Bateson believed strongly that Mendel’s work required new ways of thinking about evolution. He was one of Mendel’s earliest and fiercest defenders. Also see Rediscovery.

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                                    • Dubec, K., and Vítĕzslav Orel. 1980. Gregor Mendel’s activities in meteorology. Folia Mendeliana 65:215–242.

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                                      Mendel had a lifelong interest in meteorology, as described in this article.

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                                      • Dunn, L. C. 1965. Mendel, his work and his place in history. Special issue: Commemoration of the publication of Gregor Mendel’s pioneer experiments in genetics. Proceedings of the American Philosophical Society 109.4: 189–198.

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                                        Dunn writes that Mendel’s “sharp and clear description” (p. 193) and new interpretation of the cause of tornadoes, was overlooked for many years, only to be reinvented long hence. Available online for purchase or by subscription. Also see Life.

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                                        • Mendel, Gregor. 1866. Versuche über pflanzenhybriden. Verhandlungen des naturforschenden Vereines in Brünn. 4:3–47.

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                                          Mendel’s report of his pea experiments, in German. Mendel compiled his two lectures on his work into this paper.

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                                          • Mendel, Gregor. 1901. Experiments in plant hybridization. Journal of the Royal Horticultural Society 26:1–32.

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                                            An English translation of Mendel’s 1866 paper on peas. Available online, annotated by Roger B. Blumberg.

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                                            • Mendel, Gregor. 1950. Letters to C. Naegeli (1866–1873). Genetics 35.5, pt. 2: 1–29.

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                                              Letters from Mendel to the Swiss botanist, Karl Wilhelm von Nägeli, in which he describes his experiments on peas as well as the results of his work with other plants, as suggested by Nägeli. Available online.

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                                              • Orel, Vítĕzslav. 1996. Gregor Mendel: The first geneticist. Translated by Stephen Finn. New York: Oxford Univ. Press.

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                                                A renowned Mendel scholar describes Mendel’s work with peas. He describes the growth of Mendel’s thinking, the development of his ideas about heredity, and places his work in historical and social context. Also see Biographies, Life, and Eugenics.

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                                                Rediscovery

                                                Any biography of Mendel covers the history of how his work was essentially ignored until its rediscovery by works of three European scientists in 1900: de Vries 1900, Correns 1950, and Tschermak 1900, although the importance of Tschermak 1900 has been called into question by Monaghan and Correns 1986. Campbell 1980 expresses some question about whether de Vries independently discovered these laws himself or instead had read Mendel’s paper first. Corcos and Monaghan 1990 attempts to demythologize Mendel, suggesting that he did not understand the importance of his findings and thus did not earn the place in history that he has been given. Bateson 1902 (cited under the Debate Over the Lag in Recognition of Mendel’s Work) and Bateson and Saimders 1902 reflect the efforts of British geneticist William Bateson to bring Mendel’s work to the notice of the scientific world. Bateson was one of the first scientists to believe strongly in the importance of Mendel’s findings.

                                                • Bateson, William, and E. R. Saimders. 1902. The facts of heredity in the light of Mendel’s discovery. Reports to the Evolution Committee of the Royal Society of London 1:125–160.

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                                                  William Bateson was one of the most outspoken supporters of Mendelism and gradualism in the debate whether Mendel’s work was compatible with evolution. Here he reinterprets what is known about heredity, given Mendel’s findings. Also see Work.

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                                                  • Campbell, Margaret. 1980. Did de Vries discover the law of segregation independently? Annals of Science 37.6: 639–655.

                                                    DOI: 10.1080/00033798000200441Save Citation »Export Citation »E-mail Citation »

                                                    More on the ongoing debate over whether de Vries had read Mendel before he claimed to have discovered the same principles of heredity himself. Campbell argues that de Vries did not see Mendel’s paper until 1900 and in fact made the discovery independently. Available online for purchase or by subscription.

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                                                    • Corcos, Alain F., and Floyd V. Monaghan. 1990. Mendel’s work and its rediscovery: A new perspective. Critical Reviews in Plant Science 9.3: 197–212.

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                                                      The authors question the “myth of Mendel’s work” (p. 197), suggesting he did not earn the title of Father of Modern Genetics because he did not understand what his work actually meant about heredity. Available online for purchase or by subscription.

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                                                      • Correns, Carl. 1950. G. Mendel’s law concerning the behavior of progeny of varietal hybrid. Genetics 35.5, pt. 2:33–41.

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                                                        Correns, one of the rediscoverers of Mendel, announces that he thought he had made a new discovery in his own hybridization experiments with maize and peas but, on reading de Vries’ work, was made aware that Mendel had made the discoveries before them both. Originally published in 1900 as “G. Mendel’s Regel Über Das Verhalten Der Nachkommenschaft Der Rassenbastarde,” Berichte der deutschen botanischen Gesellschaft 18:158–168. Available online.

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                                                        • De Vries, H. 1900. Sur la loi de disjonction des hybrides. Comptes Rendus de l’Academie des Sciences 130:845–847.

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                                                          De Vries says here that all traits are made of distinct units that can be studied by experiments with hybridization. From his own work he discovered, as did Mendel, that traits are not blends of parental traits but distinct. First published in English in 1950 as “Concerning the Law of Segregation of Hybrids,” Genetics, 35.5, pt. 2: 30–32. Available online.

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                                                          • Monaghan, Floyd V., and Alain F. Correns. 1986. Tschermak: A non-discoverer of Mendelism. I. An historical note. Journal of Heredity 77.6: 468–469.

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                                                            Monaghan and Correns argue that Tschermak does not deserve to be considered one of the rediscovers of Mendel. Available online for purchase or by subscription.

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                                                            • Tschermak, Erich von. 1900. Ueber künstliche kreuzung bei Pisum sativum. Berichte der Deutschen Botanischen gesellschaft 18:232–239.

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                                                              The paper in which Tschermak announces his own results from crossing plants to determine the vigor of the offspring. He notes that, like Correns and de Vries, he, too, thought he had discovered something new. First published in English in 1950 as “Concerning Artificial Crossing in Pisum sativum,” Genetics 35.5, pt. 2: 42–47. Available online.

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                                                              The Debate over the Lag in Recognition of Mendel’s Work

                                                              The reason that Mendel’s work went unnoticed for so long has been debated. Bateson 1902, Gaskings 1959, and Moore 2001 describe three possible explanations. The first is that science was not yet ready to understand its importance, and forty years had to pass before enough was known about biology that Mendel’s work could be viewed as meaningful. A second explanation is that the paper appeared in an obscure publication, in German, which many notable scientists would not have seen. Finally, Moore 2001 argues that Mendel’s work was only important because the rediscoverers reinterpreted it to make it so.

                                                              • Bateson, William. 1902. Mendel’s principles of heredity. A defence. London: Cambridge Univ. Press.

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                                                                Because Bateson was the first outspoken supporter of Mendelism, he is said by some to be the actual rediscoverer of Mendel. He describes the problem of understanding heredity in this book, as well as how Mendel’s work moves the field forward. He believed that Mendel was ignored because the scientific world was distracted by controversy over Darwin’s Origin of Species. Also see Work.

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                                                                • Gaskings, Elizabeth B. 1959. Why was Mendel’s work ignored? Journal of the History of Ideas 20.1: 60–84.

                                                                  DOI: 10.2307/2707967Save Citation »Export Citation »E-mail Citation »

                                                                  The author suggests that Darwin’s theory of evolution had to pave the way for Mendel’s ideas on heredity. “until 1900 there was no place in the general framework of biological theory into which his work could have fitted” (p. 60).

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                                                                  • Moore, R. 2001. The “rediscovery” of Mendel’s work. Bioscene 27.2: 13–24.

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                                                                    Moore suggests that Mendel’s paper was known before 1900 and was recognized as ordinary science, but it became famous as a result of a dispute between de Vries and Correns as to which of the two had discovered the laws of heredity first.

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                                                                    Mendel’s Laws

                                                                    Mendel’s conclusions were subsequently formalized into two laws; the First Law, the Law of Segregation, and the Second Law, the Law of Independent Assortment. Mawer 2006 describes the laws clearly and succinctly. In addition, these laws are discussed in any introductory genetics or even biology textbook. A third conclusion was that all offspring in the first generation are alike: When Mendel first crossed his plants, the resulting offspring all had what he called the dominant trait, with recessive traits only reappearing in subsequent generations. This result is contained within the definition of dominance and so usually is not considered a separate law. The second law worked because Mendel’s chosen traits were, fortuitously, not closely linked on the same chromosome, so that they essentially assorted independently. Bateson 1902 (cited under Work) was one of the first to describe Mendel’s principles.

                                                                    Interest in Hybridization and Heredity Before Mendel

                                                                    Gliboff 1999 and Orel and Wood 2000 place Mendel within the historical context in which he carried out his experiments on peas. These works are of interest because they help to elucidate Mendel’s own motivation. Orel 2009 writes that selective breeding had long been carried out by farmers worldwide; in the 18th and 19th centuries in Europe, sheep were being bred for their wool for the newly developing textile industry, and farmers were learning to breed for desired characteristics. Orel and Wood 2000 describes the agriculture and agricultural sciences being promoted in Moravia in the early 1800s. They note that the 1839 Berlin-Potsdam Congress of German Agriculturalists and Foresters had met in Brno and that the abbot of the Augustinian abbey to which Mendel belonged was the organizer. In particular, sheep breeding was of special interest to farmers in the area, but, Orel 1973 says, fruit breeding was as well. Roberts 1929 describes the history of plant breeding from the beginnings to agriculture to 19th century plant breeding experiments, including Mendel’s experiments with peas. The fact that interest in breeding in general was evident locally has led some scholars to suggest that Mendel’s interest was in questions of hybridization, in breeding plants for chosen traits, not heredity per se.

                                                                    • Gliboff, Sander. 1999. Gregor Mendel and the laws of evolution. History of Science 37(pt. 2, 116): 217–235.

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                                                                      The history of botany in the 19th-century Austrian Empire and the influence of other plant breeders on Mendel’s thinking.

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                                                                      • Orel, Vítĕzslav. 1973. Interest in hybridization in Moravia before Mendel came to Brno. Journal of Heredity 64.1: 51–52.

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                                                                        A brief description of the context within which Mendel did his work. Interest in hybridization was widespread among animal and plant breeders around Brno by the time Mendel was thinking about his peas. Indeed, Mendel studied with the man who had written a book on the science of agriculture. Available online for purchase or by subscription.

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                                                                        • Orel, Vítĕzslav. 2009. The “useful questions of heredity” before Mendel. Journal of Heredity 100.4: 421–423.

                                                                          DOI: 10.1093/jhered/esp022Save Citation »Export Citation »E-mail Citation »

                                                                          Orel writes of British sheep farmer, Robert Bakewell, who systematically bred Spanish Merino sheep for wool, rearing them all under identical conditions and selecting for such characteristics as efficient weight gain. Bakewell’s methods increased interest in Merino breeds throughout Europe, including in Moravia, and scientific approaches to sheep breeding grew as did interest in avoiding the problems caused by inbreeding.

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                                                                          • Orel, Vítĕzslav, and Roger J. Wood. 2000. Scientific animal breeding in Moravia before and after the rediscovery of Mendel’s theory. Quarterly Review of Biology 75.2 (June): 149–157.

                                                                            DOI: 10.1086/393378Save Citation »Export Citation »E-mail Citation »

                                                                            Moravian sheep breeders looked to science for knowledge about breeding their animals for desirable characteristics. The Sheep Breeders’ Society, founded in 1814, decided that understanding heredity was its research goal. This article supplies this history, as well as the role of the Abbot of the Augustinian Abbey. However, “Mendel’s experiments represented a radical advance” (p. 149). Available online for purchase or by subscription.

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                                                                            • Roberts, Herbert F. 1929. Plant hybridization before Mendel. Princeton, NJ: Princeton Univ. Press.

                                                                              DOI: 10.5962/bhl.title.4517Save Citation »Export Citation »E-mail Citation »

                                                                              In a carefully researched and beautifully illustrated volume, the author documents plant breeding from the beginnings of agriculture, with a particular focus on the date palm in Mesopotamia, through 19th-century hybridization experiments, including Mendel’s work and its rediscovery. Roberts devotes his concluding chapter to Bateson’s (e.g., see Bateson 1902, cited during Work) contributions to genetics.

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                                                                              Lingering Questions

                                                                              Mendel died in relative obscurity, and Mawer 2006 describes how most of his papers, including notes, all his records of his experiments, personal papers and letters, were burned not long after his death. Thus, other than those in the papers published in 1865, the details of his experiments have been lost. This loss has led to considerable controversy, including the question of whether his statistics were too good to be true, what his motivation was in doing his experiments, what he knew and thought about evolution, and whether he actually understood what he had discovered about inheritance. These issues have been the subject of many books and papers over the last century. For example, Fisher 1936 in particular suggests that Mendel altered his data to suit his preconceived notions of what he wanted to find. Olby 1979 writes that if being a Mendelian means that one believes in the “existence of a finite number of hereditary elements which in the simplest case is two per hereditary trait, only one of which may enter a germ cell, then Mendel was clearly no Mendelian” (p. 68). Callender 1988 suggests that Mendel would not have accepted Darwinian descent with modification from a common ancestor. Monaghan and Corcos 1990 argues, as do others, that Mendel was interested in hybridization rather than inheritance. Falk and Sarkar 1991 takes objection to this assessment, while later Corcos and Monaghan 1993 makes the case again. Hartl and Orel 1992 expertly addresses each of these lingering questions. What Mendel actually knew about what he discovered, or its place in evolutionary theory will never be known in any further detail than already possible, but authors certainly still debate the issue.

                                                                              • Callender, L. A. 1988. Gregor Mendel: An opponent of descent with modification. History of Science 26:41–57.

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                                                                                Callender sees Mendel not as a Darwinian, but as a proponent of the modified doctrine of special creation, an idea attributed to the 17th-century systemist, Carolus Linnaeus. That is, he suggests that Mendel believed that hybrids were constant and unchanging. For decades after Mendel’s work was rediscovered, this latter fact was widely held to cast doubt on the idea that genetic variation was the basis of evolution.

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                                                                                • Corcos, Alain F., and Floyd V. Monaghan. 1993. Gregor Mendel’s experiments on plant hybrids: A guided study. New Brunswick, NJ: Rutgers Univ. Press.

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                                                                                  The authors attempt to demythologize Mendel, to clarify what he actually claimed to have discovered, and his motivation in doing his work. They write, for example, that he was clearly attempting to understand hybrids, not heredity per se, and that it is perplexing that he became known for the latter.

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                                                                                  • Falk, Ralph, and Sahortra Sarkar. 1991. The real objective of Mendel’s paper: A response to Monaghan and Corcos. Biology and Philosophy 6.4: 447–451.

                                                                                    DOI: 10.1007/BF00128714Save Citation »Export Citation »E-mail Citation »

                                                                                    The authors dispute the claim by Monaghan and Corcos 1990 that Mendel’s interest was in hybridization rather than inheritance. Available online for purchase or by subscription.

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                                                                                    • Fisher, R. A. 1936. Has Mendel’s work been rediscovered? Annals of Science 1.2: 115–137.

                                                                                      DOI: 10.1080/00033793600200111Save Citation »Export Citation »E-mail Citation »

                                                                                      Fisher not only questions Mendel’s statistic, but asks what he had been trying to discover, what he did discover, and what he thought he discovered. Fisher’s doubts about Mendel began decades of rethinking about Mendel’s work and its place in the history of genetics. Available online for purchase or by subscription. Also see Cheating Controversy.

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                                                                                      • Hartl, Daniel L., and Vítĕzslav Orel. 1992. What did Gregor Mendel think he discovered? Genetics 131.2:245–253.

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                                                                                        An excellent and detailed consideration of the truth and the mythology surrounding Mendel’s legacy. The authors address all of the lingering questions about Mendel’s motivation, what he thought he discovered, and so on.

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                                                                                        • Mawer, Simon. 2006. Gregor Mendel: Planting the seeds of genetics. New York: Abrams.

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                                                                                          Mawer (p. 80) cites Mendel’s use of the word anlage, meaning element, in a letter to the Swiss botanist, Karl Wilhelm von Nägeli, describing the inheritance of sex in the Lychnis species (a flowering plant). Mawer suggests that this exchange makes it clear that Mendel understood that he had discovered that inheritance is due to discrete particles, which soon came to be known as genes. Published in association with the Field Museum, Chicago. Also see Biographies, Life, and Mendel’s Laws.

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                                                                                          • Monaghan, Floyd V., and Alain F. Corcos. 1990. The real objective of Mendel’s paper. Biology and Philosophy 5.3: 267–292.

                                                                                            DOI: 10.1007/BF00165254Save Citation »Export Citation »E-mail Citation »

                                                                                            The authors argue that Mendel was not interested in understanding inheritance per se but in the laws of hybridization. Falk and Sarkar 1991 criticizes this perspective, arguing that Mendel’s interest was in inheritance. Monaghan and Corcos follow with a reply, published in 1993 as “The Real Objective of Mendel’s Paper: A Response to Falk and Sarkar’s Criticism,” Biology and Philosophy 8.1: 95–98. Both the article and their response to Falk and Sarkar are available online for purchase or by subscription.

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                                                                                            • Olby, Robert. 1979. Mendel, no Mendelian? History of Science 17:53–72.

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                                                                                              Olby puts Mendel into historical context. He describes Mendel’s primary interest as in hybridization, and he reminds his readers of the rudimentary understanding of heredity of the time and that thus Mendel could not have understood the importance of his findings.

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                                                                                              Cheating Controversy

                                                                                              Fisher 1936 raises the question of whether Mendel’s statistics were too good to be true and, if so, whether he intentionally cooked his numbers. Van der Waerden 1968 cites Fisher’s famous final verdict on the controversy that he himself stirred up: “The data have evidently been sophisticated systematically, and after examining various possibilities, I have no doubt that Mendel was deceived by a gardening assistant, who knew too well what his principal expected from each trial made” (pp. 281–282). This question has been revisited numerous times, including by Di Trocchio 1991; Franklin, et al. 2008; and Novitski 2004, but it has generally been resolved in Mendel’s favor. Weiss 2002 argues that Mendel’s training in physics may have influenced how he interpreted his data. Fairbanks and Rytting 2001 is a thorough reexamination of both sides of this question. Westerlund and Fairbanks 2004 argues that Mendel made it clear in his paper what he did and what he understood.

                                                                                              • Di Trocchio, Federico. 1991. Mendel’s experiments: A reinterpretation. Journal of the History of Biology 24.3:485–519.

                                                                                                DOI: 10.1007/BF00156322Save Citation »Export Citation »E-mail Citation »

                                                                                                The author writes that it is impossible to understand from his paper what Mendel really did. Available online for purchase or by subsciption.

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                                                                                                • Fairbanks, Daniel J., and Bryce Rytting. 2001. Mendelian controversies: A botanical and historical review. American Journal of Botany 88.5 (May):737–752.

                                                                                                  DOI: 10.2307/2657027Save Citation »Export Citation »E-mail Citation »

                                                                                                  An excellent thorough reexamination of the issues. The authors conclude that Fisher (see Fisher 1936) overstated the case in part because he misinterpreted Mendel’s description of what he did. Available online for purchase or by subscription.

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                                                                                                  • Fisher, R. A. 1936. Has Mendel’s work been rediscovered? Annals of Science 1.2: 115–137.

                                                                                                    DOI: 10.1080/00033793600200111Save Citation »Export Citation »E-mail Citation »

                                                                                                    Fisher presents what he believed was evidence that Mendel’s data were not only too good to be true but “cooked.” Available online for purchase or by subscription. Also see Lingering Questions.

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                                                                                                    • Franklin, Allan, A. W. F. Edwards, Daniel J. Fairbanks, Daniel L. Hartl, and Teddy Seidenfeld. 2008. Ending the Mendel–Fisher controversy. Pittsburgh, PA: Univ. of Pittsburgh Press.

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                                                                                                      A through exploration of Fisher’s rationale for thinking Mendel’s data were cooked. The authors conclude that Fisher overstated his case.

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                                                                                                      • Novitski, Charles E. 2004. Revision of Fisher’s analysis of Mendel’s garden pea experiments. Genetics 166.3: 1139–1140.

                                                                                                        DOI: 10.1534/genetics.166.3.1139Save Citation »Export Citation »E-mail Citation »

                                                                                                        Novitski takes exception to Fisher’s criticisms of Mendel’s work, while accepting that perhaps “many of Mendel’s results are surprisingly close to the theoretical expectation” (p. 1140).

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                                                                                                        • Van der Waerden, B. L. 1968. Mendel’s experiments. Centaurus 12.4: 275–288.

                                                                                                          DOI: 10.1111/j.1600-0498.1968.tb00098.xSave Citation »Export Citation »E-mail Citation »

                                                                                                          Van der Waerden argues that it is not unlikely that Mendel’s experiments were valid. Available online for purchase or by subscription.

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                                                                                                          • Weiss, Kenneth. 2002. Goings on in Mendel’s Garden. Evolutionary Anthropology 11.2: 40–44.

                                                                                                            DOI: 10.1002/evan.10019Save Citation »Export Citation »E-mail Citation »

                                                                                                            A recent reconfirmation that Fisher overstated his case. Mendel was trained by developers of the atomic theory of molecules, in which each element was an integral multiple of the carbon atom. As a result, he may have been expecting integral (whole number) ratios in transmission of his heritable elements as well. Thus he may have interpreted his results in terms that made sense under that theoretical expectation. Available online for purchase or by subscription.

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                                                                                                            • Westerlund, Julie, and Daniel Fairbanks. 2004. Gregor Mendel and “myth-conceptions.” Science Education 88.5: 754–758.

                                                                                                              DOI: 10.1002/sce.20007Save Citation »Export Citation »E-mail Citation »

                                                                                                              The authors attempt to correct misconceptions about Mendel’s contributions to genetics, including with respect to what he himself understood about his findings. They suggest that Mendel made it clear what he did and what he understood and that critics should pay heed to his paper. Available online for purchase or by subscription.

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                                                                                                              Modern Evolutionary Synthesis

                                                                                                              The rediscovery of Mendel’s work did not lead to immediate acceptance, however, but was part of a larger debate over the nature of evolutionary change. Biologists questioned whether evolution occurred gradually or by leaps. Many who believed it must be gradual and a product of natural selection, as Darwin did, could not reconcile this theory with Mendel’s demonstration that there must be factors that produced discrete traits. In 1900, most known mutations (“sports” as they were called) were major and dysfunctional, and often lethal, not thought of as suitable material for adaptive evolution by natural selection. Further, mutations were thought to be very rare, while environmental change could occur at any time, suggesting that it was unlikely that there was relevant Mendelian variation from which to select. Darwin knew of sports and wrote of them in The Origin of Species in 1859 (Darwin 1859), but he did not think they were important to evolution: Many of the traits of adaptive of interest to him, which he insisted evolved almost imperceptibly slowly, were quantitative. This concept, too, seemed incompatible with Mendelian thinking. During the early 20th century, however, mutations with minor, viable effects were being identified. Further, several authors noted that Mendelian transmission of many independent genes (as his “elements” became known) that contributed to a given trait could endow that trait with a quantitative distribution in populations, and selection could work on the traits gradually. These traits are called polygenic traits. Fisher 1930 (and Ronald A. Fisher’s other work) is now taken as the exemplar of this new recognition. The result was that Mendel’s laws and the gradualism of evolution were finally accepted as compatible when population genetics, the formal mathematical modeling of genes within populations, came of age. This acceptance lead to the consensus that developed in the 1930s and was known as the Modern Synthesis, as described in Huxley 1942 and Mayr 1942, for example. The synthesis remains the current consensus. Traits may not be inherited in a Mendelian fashion, but the genetic variants contributing to them are. This understanding led to the development of formal quantitative genetics as a fundamental aspect of modern agricultural and experimental genetics and its evolutionary connections. Falconer 1960, now in its fourth edition, became a definitive text on the subject. Wright 1931 is a classic paper on the theory joining Mendelian inheritance and evolution. Wright 1968–1978 is a major four-volume compendium of the work of one of the last century’s foremost population geneticists.

                                                                                                              • Darwin, Charles. 1859. The origin of species. London: Murray.

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                                                                                                                The original book on the role of natural selection in the formation of adaptation and new species. In the early chapters he refers to his theory that traits acquired during life can be inherited.

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                                                                                                                • Falconer, Douglas S. 1960. Introduction to quantitative genetics. 1st ed. London: Oliver and Boyd.

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                                                                                                                  The first edition of what became a long-standing fundamental textbook of the genetics of quantitative traits, or traits due to the effects of many genes, and the appearance of these traits in families, the correlation of trait measures among relatives, and their response to artifical selection. Most recent edition is the fourth edition by Douglas Falconer and Trudy F. C. Mackay (Harlow, UK: Prentice Hall, 1996).

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                                                                                                                  • Fisher, Ronald A. 1930. The genetical theory of natural selection. Oxford: Clarendon.

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                                                                                                                    One of the major figures in the development of population genetics and the modern synthesis.

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                                                                                                                    • Huxley, Julian. 1942. Evolution: The modern synthesis. London: Allen and Unwin.

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                                                                                                                      Julian Huxley invented the term modern synthesis. The third edition, published in 1974 (London: Allen and Unwin), is edited by John R. Baker and includes an introduction by Baker.

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                                                                                                                      • Mayr, Ernest. 1942. Systematics and the origin of species: From the viewpoint of a zoologist. New York: Columbia Univ. Press.

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                                                                                                                        Biologist Ernst Mayr was an active player in the unification of the two sides of the gradualism/saltation debate.

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                                                                                                                        • Wright, Sewall. 1931. Evolution in Mendelian populations. Genetics 16.2:97–159.

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                                                                                                                          One of the leaders of evolutionary genetics’ classic papers explaining how evolution and Mendelian inheritance work together as a function of population structure and other evolutionary factors. Available online.

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                                                                                                                          • Wright, Sewall. 1968–1978. Evolution and the genetics of populations: A treatise. 4 vols. Chicago: Univ. of Chicago Press.

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                                                                                                                            A four-volume classic, a compendium of Wright’s thinking and work on population genetics and evolution.

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                                                                                                                            Mendelian Genetics

                                                                                                                            Mendel’s Laws are his lasting legacy, the theory of how traits are inherited from parent to offspring. Mendel proposed that every individual carries two factors, now called genes, for each trait. The factors may determine identical or differing forms of the trait, and how many can be expected of each form is predictable. Most modern genetics textbooks present genetics as Mendelian, and much of modern genetics is based on the assumption that there are single or a few major genes for traits. For many decades in the 20th century, specific genes were unknown or difficult to identify and the nature of DNA was unknown. Human genetics, in particular, could not be approached experimentally, so that Mendelian principles were used to identify traits that were shared by family members and hence might be genetic. This approach began with Garrod 1908 on the appearance of metabolic diseases in consanguineous relatives (cousins) as predicted from Mendelian principles. A field called segregation analysis developed to use statistical methods to see if traits appeared in families in ways consistent with Mendel’s rules. This method of analysis led to the clinical field of genetic counseling to advise members of affected families of risks to relatives, which was a main aspect of human genetics in the mid-20th century. Stern 1973 is a classic human genetics text that shows the importance of Mendelian disease before causal genes could be identified. Stevenson, et al. 1976 is a midcentury text that stresses methods for the evaluation of risk of genetic disease, especially Mendelian disorders, which segregate in families following Mendel’s principles. Speicher, et al. 2009 is the fourth edition of a textbook of human genetics, including Mendelian genetics, written by major figures in the field. Genetic counseling included the development of sophisticated Bayesian statistics in the process to alter risk estimates based on the trait presence or absence in each newly observed person in a family, as described in Murphy and Chase 1975. In the computer era, Cannings, et al. 1978 and Elston and Stewart 1971 show how it was possible to do segregation analysis on open-ended numbers of arbitrarily complex families with readily available software. However, Edwards 1960 shows that complex traits due to many contributing genes can appear to simulate Mendelism in terms of risk and appearance in close family members, points that are not widely appreciated. Subsequently, technology has made it possible to find genes contributing to disease without direct reliance on segregation analysis, with a method called genomewide association studies, with segregation patterns of identified candidate alleles in families as a confirmatory follow-up.

                                                                                                                            • Cannings, C., E. A. Thompson, and M. H. Skolnick. 1978. Probability functions on complex pedigrees. Advances in Applied Probability 10:26–61.

                                                                                                                              DOI: 10.2307/1426718Save Citation »Export Citation »E-mail Citation »

                                                                                                                              An early article explaining a theoretical method for doing Mendelian segregation analysis in arbitrarily large pedigrees that could even include inbreeding “loops.” Available online for purchase or by subscription.

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                                                                                                                              • Edwards, J. H. 1960. The simulation of Mendelism. Acta Genetica et Statistica Medica 10.1–3: 63–70.

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                                                                                                                                Paper showing that the appearance of a polygenic trait (caused by many genes) could appear to segregate in a Mendelian way among close family members. Available online for purchase or by subscription.

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                                                                                                                                • Elston, R. C., and J. Stewart. 1971. A general model for the analysis of pedigree data. Human Heredity 21.6: 523–542.

                                                                                                                                  DOI: 10.1159/000152448Save Citation »Export Citation »E-mail Citation »

                                                                                                                                  The first, or one of the first, articles to show a general method for doing Mendelian segregation analysis in arbitrarily complex pedigrees. Available online for purchase or by subscription.

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                                                                                                                                  • Garrod, Archibald E. 1908. The Croonian lectures on inborn errors of metabolism. Lancet 172.4427:1–7.

                                                                                                                                    DOI: 10.1016/S0140-6736(01)78482-6Save Citation »Export Citation »E-mail Citation »

                                                                                                                                    The pioneering book of modern human genetics, recognizing single-gene recessive disorders (here, metabolic disease) and their appearance in relatives in consanguineous families. Available online for purchase or by subscrption. Lectures continue in subsequent issues: Lancet 172.4428: 73–79; Lancet 172.4429: 142–148; and Lancet 172.4420: 214–220, also available for purchase or by subscription.

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                                                                                                                                    • Murphy, Edmond A., and Gary A. Chase. 1975. Principles of genetic counseling. Chicago: Year Book Medical.

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                                                                                                                                      An important book on methods for using various types of analysis to estimate risk in families and identify potential Mendelian modes of inheritance.

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                                                                                                                                      • Speicher, Michael R., Stylianos E. Antonarakis, and Arno G. Motulsky, eds. 2009. Vogel and Motulsky’s human genetics: Problems and approaches. 4th ed. Heidelberg, Germany: Springer.

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                                                                                                                                        Recent edition of a major attempt at a comprehensive text on genetic traits in humans.

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                                                                                                                                        • Stern, Curt. 1973. Principles of human genetics. 3d ed. San Francisco: Freeman.

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                                                                                                                                          A mid-century classic on human genetics, showing the importance of Mendelian analysis at a time when very few genes could actually be identified.

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                                                                                                                                          • Stevenson, Alan C., Brigid C. C. Davison, and Michael W. Oakes. 1976. Genetic counseling. 2d ed. Philadelphia: Lippincott.

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                                                                                                                                            A major text of mid-century human genetics, stressing the evaluation of risk of genetic disease, especially Mendelian disorders (that segregate in families following Mendel’s principles).

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                                                                                                                                            Limitations of Mendelism

                                                                                                                                            Mendelian genetic inheritance has been confirmed repeatedly in diploid species, but it seems often to be somewhat misinterpreted. Some traits and some diseases are determined by single genes, as Mendel’s pea color or pea plant height illustrated. In those instances, it is pragmatic to think of the trait itself as being inherited in a Mendelian way. In truth, of course, the genetic variants (alleles) are inherited in that way, while the trait itself only arises in the offspring’s development. In these cases, the trait tracks the presence of the responsible alleles in families (as Mendel observed in peas). For decades this formed the basis of experimental approaches that led to our modern understanding of DNA and genetic function. That path of inquiry was one of the most powerful and successful methodological approaches in the history of science. However, as more has been learned about genes, it has become clear that Mendel’s Laws describe only a subset of the ways in which traits are patterned in populations or families and the genetic basis of trait formation. The lasting informal interpretation of Mendel is a conceptual legacy that sees genes as being “for” traits and traits made by single genes or only a few. This concept has been misleading in many respects, because most traits are produced by multiple genes in concert, often interacting with environmental conditions, as seen in Bonduriansky 2012, Weiss 2011, and Weiss and Buchanan 2011.

                                                                                                                                            Non-Mendelian Factors in Inheritance

                                                                                                                                            Quantitative geneticists have known since the early 20th century that important traits are due to what were nonenumerable, large numbers of genes contributing individually minor effects. Even for simpler traits, more recently much work has been done on modifier genes, that is, genes that affect the expression of other genes. Hamilton and Yu 2012, the influential work of Jablonka and Lamb 2005, and more recently Jablonka and Lamm 2012, among many others, suggest that epigenetics—that is, heritable changes in gene expression due to mechanisms other than changes in DNA sequence—has more effect on traits than previously understood. In addition, the idea that genes are always either dominant or recessive has been shown to be a limited view of the manner in which genotype leads to phenotype. Weiss and Buchanan 2011, among many others, points out that while a trait—for example, the presence or absence of a disease—may be due to the effects of a single gene, it is typical that in the population there are numerous variants of that gene, along with effects of environment or other genes, so that the simple dominance relations are inaccurate and should be replaced by a more modern understanding of the quantitative relation between genotype and phenotype. Scriver 2007 uses a disease called phenylketonuria as an example, and Weatherall 2000 describes the genetic basis of resistance to malaria as an example. Furthermore, Pigliucci 2007 is just one of many evolutionary biologists who believe it is time for an extended evolutionary synthesis that goes beyond the theory of the gene to include theories of form. That is, what needs to be explained is not how genes work but how organisms are formed, the motivation behind the relatively new field of evolutionary development, commonly known as EvoDevo.

                                                                                                                                            Eugenics

                                                                                                                                            There are many issues that are of interest in regard to Mendel’s work in his time. After considerable investigation, it seems that Mendel read and marked up a German translation of Darwin’s Origin of Species (Darwin 1859, cited under Modern Evolutionary Synthesis), but he did not think it very pertinent to his own work. He questioned Darwin’s idea of gradual or blending inheritance, which differed from the discrete inheritance he was working on in pea hybrids, and he was not interested long-term evolution (of new species). Darwin had two books in German that referred to Mendel, but in the main one the pages had not been cut and the evidence, as reviewed by Orel 1996 and others, is that Darwin was not aware of Mendel’s work. Likewise, Mendel lived in an era when both his work and Darwin’s were beginning to be used by various people to justify value-laden theories of inherent worth, which was plausible based on the observation that some human traits followed Mendel’s rules of inheritance. But Mendel was not involved in these controversies. Carlson 2001 is a useful modern overview of the history of eugenics. Davenport 1911 is an early example of a widely read volume on the subject, written by one of the leaders of the American eugenics movement, and Baur, et al. 1931, a widely used textbook at the time, is another, used to justify the Holocaust.

                                                                                                                                            • Baur, Erwin, Eugen Fisher, and Fritz Lenz. 1931. Human heredity. Translated by Eden and Cedar Paul. London: George Allen and Unwin.

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                                                                                                                                              The leading textbook for twenty years, in four editions, on human genetics or “racial hygiene,” that was used to justify the Holocaust. After Hitler took power, the book was used as the scientific basis for eugenic sterilization and other Nazi methods.

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                                                                                                                                              • Carlson, Elof A. 2001. The unfit: A history of a bad idea. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.

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                                                                                                                                                Carlson documents the history of eugenics and its role in the Holocaust.

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                                                                                                                                                • Davenport, Charles B. 1911. Heredity in relation to eugenics. New York: Holt.

                                                                                                                                                  DOI: 10.5962/bhl.title.29389Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                  Written by a prominent American biologist and a leader of the American eugenics movement, this book promotes a racist genetic determinism and was widely read including as a text in medical schools.

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                                                                                                                                                  • Orel, Vítĕzslav. 1996. Gregor Mendel: The first geneticist. Translated by Stephen Finn. New York: Oxford Univ. Press.

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                                                                                                                                                    An excellent biography of Mendel, written by a resident of Brno and historian of science. Also see Biographies, Life, and Work.

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