Without being really noticed by contemporary scientists,
the book titled Versuche über Pflanzen-Hybride
(Treatises on Plant Hybrids) and written by the Austrian (Moravian-Silesian)
Augustinian monk Gregor Mendel appeared in 1865. Mendels treatise described
his observations on the inheritance of various characteristics ("factors")
in cross-bred pea plants as manifested in the phenotypes of subsequent generations.
as Mendels Laws, his famous principles of hereditary transmission were
to revolutionise the cultivation of plants and
the breeding of domesticated animals in the twentieth century.
Biochemistry and molecular biology have found the molecular basis of
Mendels Laws in form of gene expression in cells and gene transmission in the germline.
Mendels work made it possible for
the first time to exploit the genetic resources of organisms systematically.
Mendels name marks not only the beginning of genetics as a scientific
discipline in its own right but also the beginning of the systematic use
of mathematics, quantified measurements and applied statistics in biology.
Without being really noticed by contemporary scientists, the book titled Versuche über Pflanzen-Hybride (Treatises on Plant Hybrids) and written by the Austrian (Moravian-Silesian) Augustinian monk Gregor Mendel appeared in 1865. Mendels treatise described his observations on the inheritance of various characteristics ("factors") in cross-bred pea plants as manifested in the phenotypes of subsequent generations. Later known as Mendels Laws, his famous principles of hereditary transmission were to revolutionise the cultivation of plants and the breeding of domesticated animals in the twentieth century. Biochemistry and molecular biology have found the molecular basis of Mendels Laws in form of gene expression in cells and gene transmission in the germline. Mendels work made it possible for the first time to exploit the genetic resources of organisms systematically. Mendels name marks not only the beginning of genetics as a scientific discipline in its own right but also the beginning of the systematic use of mathematics, quantified measurements and applied statistics in biology.
Mendel at the University in Vienna
Gregor Mendel was born on either 20th or 22nd July, 1822 in Heizendorf (today Hynice in the Czech Republic), a village near the border between northern Moravia and Silesia. From 1851 to 1853, Gregor Mendel studied zoology, botany, chemistry, and physics at the University of Vienna. He became a member of the Zoologico-Botanical Society of Austria and has published two scientific treatises in the "Verhandlungen" of this scientific organization (1853 and 1854). Probabely due to health reasons (epilepsia ?), Mendel has returned to Brno without formally finishing the University in Vienna.
Experimentation in the monastery garden results in laws of inheritance ...
With the support of the Abbot of the Augustinian monastery in Brno, Cyrill Franz Napp, who took a lively interest in the natural sciences and plant cultivation, Mendel began his experiments with the hybrid cultivation of pea plants in 1856. After spending eight years carrying out experimental work in the monastery garden, he reported on the results of his observations at the meetings of the Association for Natural Research in Brno on the evenings of February 8th and March 8th, 1865. The Association published the written accounts of these observations in 1866, under the title Versuche über Pflanzen-Hybride. They appeared in Volume 4 of the Associations records, Verhandlungen des naturforschenden Vereines in Brünn.
|The garden of the Augustinian Convent in Brno. This view is looking towards the entrance to the garden, with Mendlovo namesti, Mendel Square, beyond. In the shadows in front of the tree can just be seen part of the foundations of the greenhouse that Mendel used. His peas were planted in the beds against the building on the left.|
|The same area in a photograph dating from the 1920s. This view is looking in the opposite direction and shows a close up of the garden area that can be seen in the shadows of the building in the previous photo. It is precisely here that Mendel grew his peas.|
... but there was little reaction from the scientific community
We know from contemporary written reports that the audience received Mendels lectures courteously but with blank incomprehension. He must have been bitterly disappointed at the indifference with which his revelations were greeted. Mendels approach and the nature of his experimentation were simply too unconventional for his age. Nobody before him had ever attempted to use mathematical and statistical analysis as a means of interpreting the results of biological inquiry. Additionally, Mendel was known as a relatively shy person and might not have presented his results with the necessary emphasis and stress. Another reason for the absence of any response from the scientific fraternity of the day will have been the limited number of people who read the Brno Associations records. Mendel asked one of his fellow monks to send forty special reprints to botanists and other distinguished scientific figures known to be interested in the hybridisation of plants. Nine of these reprints have so far come to light. One of the recipients was Carl Wilhelm von N?geli, probably the most highly acclaimed botanist of the mid-nineteenth century, who was then teaching in Munich. He was the only one of the forty who was prompted to embark on an extended correspondence with Mendel. However, it appears likely that Nägeli had only glanced at the reprint because although it in fact dealt with no fewer than 355 cross-bred strains and 12,980 resultant hybrids he described Mendels work as "incomplete" and urged him to carry on with his experiments. Nägeli also offered Mendel "fatal" advice: to continue his investigations using the hawkweed (Hieracium), a plant belonging to the family of the asters. It was only later that botanists discovered these plants asexual reproduction, which meant that experiments in hybridisation with hawkweed were bound to be inconclusive, since the genetic information is transferred exclusively via the maternal line.
The tragedy of a brilliant scientist
At this stage Mendel abandoned the clearly delineated approach which had been a feature of his published investigations of hybridisation in garden pea plants. The lack of response to his publication and the failure of his experiments with hawkweed induced him to devote less time to his scientific work. His unanimous election as Abbot in 1868 afforded only partial compensation for his disappointment. His hopes of being able to resume his experiments were dashed by the sheer work load entailed in running the monastery. In 1883, only a matter of months before his death in the following year, Mendel commented, with a hint of resignation mingled with the awareness of the importance of his discoveries: "My scientific studies have afforded me great gratification; and I am convinced that it will not be long before the whole world acknowledges the results of my work." Modern-day research has shown that Mendel did not work in isolation but that the monastic community included other distinguished scholars. These men not only knew of and understood the nature of Mendels work but also regarded it as very important. Had Mendels experiments been viewed as mere "whimsicality", then he would have been dismissed as a "freethinker" devoid of the slightest incentive to vindicate the churchs dogmas. In this case Mendel would hardly have been elected Abbot only two years after the publication of his "Treatises".
The rediscovery of Mendels Laws
However, it was to take thirty-four years before Mendels prediction came true. The year 1900 saw the now famous rediscovery of Mendels Laws by Carl Correns in Germany, Hugo de Vries in the Netherlands and Erich von Tschermak-Seysenegg in Austria. Their achievement was to realise that Mendel had not merely conducted experiments in successful hybridisation but had in fact studied the heredity of specific characteristics as they were passed on from parent plants to their offspring.
Did Mendel work correctly ? I. Statistics of offspring data
As Mendels fundamental insights into the principles of heredity in plants and animals came to be used on an ever wider basis, and with the advent of variation statistics, the numerical proportions which Mendel had deduced from his experiments came under fire. In 1936, for instance, the British mathematician R.A. Fisher prompted a discussion of the question whether Mendel had adjusted the observed segregation ratio to accommodate his predictions - in other words, whether he had falsified his results. Fisher based his argument on the supposition that Mendels segregation ratios were far higher than the principles of variation statistics would permit. Such segregation ratios, Fisher asserted, could occur only very seldom. In 1968 the Austrian-Swedish genetic scientist H. Lamprecht disproved Fishers assertions. Lamprechts own experiments with the hybridisation of pea plants produced segregation ratios that in some cases even more closely matched the expected values. In 1983 the German doctor and botanist F. Weiling conducted biometric experiments which showed that Fishers studies had in several instances been based on erroneous or inapposite statistical assumptions. Only a few weeks ago J. Vollmann, working at the Institute of Plant Structure and Plant Breeding at Viennas University of Soil Cultivation, carried out computer simulations which showed that just thirty hybridisation simulations with a hypothetical number of 5,000 offspring produced an almost perfect match with Mendels 3:1 ratio. Analysing all of Mendels results (including those that were not published) produces a ratio of 6022:2000 with an error margin of under 1.5%.
Did Mendel work correctly ? II. Independence of characteristics
Mendels observation of the independent inheritance of characteristics also prompted critical comment. The probability of finding seven characteristics located one on each of the seven chromosomes of the garden pea is demonstrably 1:163. As we now know, two pairs of the characteristics studied by Mendel are located on chromosome 1 and chromosome 4. However, it is seldom that both characteristics are passed on together (coupling). The questions of whether Mendel was simply fortunate in his selection of characteristics, whether he had conducted preliminary experiments with certain genotypes before choosing his characteristics, and whether he came across divergent segregation ratios are currently still under discussion.
Mendels scientific achievement
Mendels outstanding intellectual achievement as a scientist was his ability to make deductions from the observed results of individual experiments in other words, to perceive a distinct pattern despite the random inaccuracies of a few observations. This enabled him, for example, to ascertain the 3:1 segregation ratio in the heredity of red and white pea flowers in the face of a diversity of possible hereditary patterns. This insight long predated the advent of biometrics or even of probability calculus.
|The Mendel memorial Mendel holds his hands out protectively over marble pea plants. Rather more moving is the fact that the plants growing at the foot of the plinth are also Pisum sativum. The previous photograph of the whole garden was taken from just beside this rather idealised statue.|
Mendel and Darwin
Mendel, so the argument goes, had set out to refute Darwins postulations and, as an exponent of a theological world view, to demonstrate that change can also occur as the result of cross-breeding.
Nineteenth-century theologians regarded Darwins "Origin of the Species" as a frontal assault on the dogma of Gods creation of mankind. It was not until 1951 that Pope Pius XII paved the way for an open discussion of evolution within the church. The truly innovative and original idea in Darwins work was the concept of population, from which the theory of natural selection proceeded. Heredity in Mendels terms, however, far from producing evolutionary change, results in perfectly predictable segregation ratios.