Gregor Mendel, OSA (1822–1884), founder of scientific genetics page 1
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Gregor Mendel, OSA (1822–1884), founder of scientific genetics

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  • PERINATAL LESSONS FROM THE PAST

    Gregor Mendel, OSA (18221884), founder of scientificgeneticsP M Dunn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    Arch Dis Child Fetal Neonatal Ed 2003;88:F537F539

    Gregor Mendel, an Augustinian monk and part-timeschool teacher, undertook a series of brilliant hybridisationexperiments with garden peas between 1857 and 1864 inthe monastery gardens and, using statistical methods forthe first time in biology, established the laws of heredity,thereby establishing the discipline of genetics.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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    Correspondence to:Professor Dunn,Department of ChildHealth, University ofBristol, SouthmeadHospital, Southmead,Bristol BS10 5BN, UK;P.M.Dunn@bristol.ac.uk

    Accepted 12 June 2003. . . . . . . . . . . . . . . . . . . . . . .

    Mendel, baptised Johannes, was born on 22July 1822 at Heinzendorf in Moravia,then part of Austria, now in the Czech

    Republic. He was the only son of strugglingpeasant farmers who also had two daughters.Initially Mendel attended the village school inHeinzendorf. There, the parish priest, JohannSchreiber, also an expert in fruit growing,recognised his talents and persuaded his parentsto continue his education in spite of their limitedresources. At the age of 12 he was sent to thegymnasium in Troppau where he studied for thenext six years. During that period, Mendelsfather was incapacitated by a falling log andbecame unable to support his son, whose healthin turn suffered. In 1840 Mendel took a two yearcourse of philosophy at the PhilosophicalInstitute of the University of Olmutz, but havingpassed the final exams in mathematics and Latinphilosophy with the highest grades, he withdrewbecause of ill health. At this point in 1842, hisyounger sister came to his aid with financialsupport while he completed an extra yearsstudy. His exam results were excellent, especiallyin mathematics and physics. In 1843 at the age of21, Mendel entered the Augustinian Order at StThomas Monastery near Brunn (now Brno), tookthe name of Gregor, and began his theologicalstudies at the Episcopal Seminary there. He wasordained to the priesthood in 1847. The role ofthe parish priest at that time in Austria extendedway beyond the care of mens souls. St ThomasMonastery was a centre of creative interest inboth science and culture, having among itsmembers well known philosophers, musicians,mathematicians, mineralogists, and botanists.During this period, Mendel was able to studyagriculture, fruit growing, and viniculture as wellas theology.13

    After ordination, Mendel was assigned first topastoral duties, and then, finding himselfunsuited to this because of his shyness, toteaching in a secondary school in Znaim.However, on failing to obtain his teacherscertificate, he was sent to the University of

    Vienna (18511853) to study natural sciencesand mathematics. It was at this time that heacquired the scientific research skills that he waslater to put to such good use. In 1854, Mendelreturned to teaching in Brunn but two years lateragain failed to obtain a teaching certificate. It issaid that he withdrew from the exam because ofnervous exhaustion; another account suggeststhat it was because of a disagreement with theexaminers in botany, a disagreement that thenprompted him later to undertake his famousplant breeding experiments. Whatever the truth,this exam failure led to Mendel becoming a part-time assistant teacher, a post that provided himwith plenty of time to undertake his scientificresearch13 (fig 1).

    Between 1857 and 1864 Mendel undertook aseries of hybridisation experiments in theMonasterys garden, which were breathtakingfor their brilliance in planning, observation, andanalysis, and in interpretation of results. He wasfortunate to choose the garden pea, Pisum, for hisstudies because it exists in separate pure lines.Within each line, each plant is identical,although each may vary in characters such ascolour or shape. In addition, peas are hermaph-rodite, bearing both male and female sex cells onthe same individual and able to self fertilise.Furthermore, the flowers are naturally selffertilised before the bud opens and thus beforeinsects can intervene in the process. In addition,the pea is an annual and great numbers can begrown in a small space. Mendel described hisproject in the following way in the introductionto his paper on Experiments in plant hybridization,which was presented to the Society for the Studyof the Natural Sciences in Brunn in 186514

    (fig 2).

    Experiments in plant hybridization5

    Experience of artificial fertilization, such asis effected with ornamental plants in order toobtain new variations in colour, had led tothe experiments which will here be discussed.The striking regularity with which the samehybrid forms always reappeared wheneverfertilization took place between the samespecies induced further experiments to beundertaken, the object of which was to followup the developments of the hybrids in theirprogeny so far, no generally applicablelaw governing the formation and develop-ment of hybrids has been successfully for-mulated of

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  • Those who survey the work done in this department willarrive at the conviction that among all the numerousexperiments made, not one has been carried out to suchan extent and in such a way as to make it possible todetermine the number of different forms under which theoffsping of hybrids appear, or to arrange these forms withcertainty according to their separate generations, ordefinitely to ascertain their statistical relations.

    It requires indeed some courage to undertake a labour ofsuch far-reaching extent; this appears, however, to be theonly right way by which we can finally reach the solutionof a question the importance of which cannot be over-estimated in connexion with the history of the evolution oforganic forms.

    The paper now presented records the results of such adetailed experiment. This experiment was practicallyconfined to a small plant group, and is now, after eightyears pursuit, concluded in all essentials. Whether theplan upon which the separate experiments were con-ducted and carried out was the best suited to attain thedesired end is left to the friendly decision of the reader.

    This research did indeed require courage and also persistenceand meticulous record keeping. In all, some 10 000 plantswere grown and observed during the eight year study. Thefollowing further extracts from his paper published in 1866provide a taste of his style and conclusions.5

    The forms of the hybrids5

    In the case of each of the seven crosses the hybrid-character resembles that of one of the parental forms soclosely that the other either escapes observation comple-tely or cannot be detected with certainty. This circumstance

    is of great importance in the determination and classifica-tion of the forms under which the offspring of the hybridsappear. Henceforth in this paper those characters whichare transmitted entire, or almost unchanged in thehybridization, and therefore in themselves constitute thecharacters of the hybrid, are termed the dominant, andthose which become latent in the process recessive. Theexpression recessive had been chosen because thecharacters thereby designated withdraw or entirelydisappear in the hybrids, but nevertheless reappearunchanged in their progeny, as will be demonstrated lateron.

    It was furthermore shown by the whole of the experimentsthat it is perfectly immaterial whether the dominantcharacter belongs to the seed-bearer or to the pollen-parent; the form of the hybrid remains identical in bothcases

    The first generation (bred) from the hybrids5

    In this generation there reappear, together with thedominant characters, also the recessive ones with theirpeculiarities fully developed, and this occurs in thedefinitely expressed average proportion of three to one,so that among each four plants of this generation threedisplay the dominant character and one the recessive. Thisrelates without exception to all the characters which wereinvestigated in the experiments. The angular wrinkled formof the seed, the green colour of the albumen, the whitecolour of the seed-coats and the flowers, the constrictionsof the pods, the yellow colour of the unripe pod, of thestalk, of the calyx, and of the leaf venation, the umbel-likeform of the inflorescent, and the dwarfed stem, allreappear in the numerical proportion given, without anyessential alteration. Transitional forms were not observedin any experiment.

    Since the members of the first generation spring directlyfrom the seed of the hybrids, it is now clear that the hybridsform seeds having one or other of the two differentiatingcharacters, and of these one-half develop again the hybridform, while the other half yield plants which remain

    Figure 1 Gregor Mendel, 18221884.

    Figure 2 The opening paragraph of Mendels 1865 paper on thehybridisation of peas.

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  • constant and receive the dominant or the recessivecharacters (respectively) in equal numbers.

    Before Mendel, heredity had been regarded as a blendingprocess and the offspring a dilution of the various parentalcharacteristics. Mendel showed that the different charactersin heredity followed specific laws, which could be determinedby counting the diverse kinds of offspring produced fromparticular sets of crosses. He established two principles ofhe