Mendel and T. H. Morgan readings

Mendel and T. H. Morgan readings - 348 displays an...

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Unformatted text preview: 348 displays an affectionate feminine attitude to his father and a corresponding jealousy and hostility towards his mother. It is this complicating element introduced by bisexuality that makes it so difficult to obtain a clear view of the facts in connection with the earliest object-choices and identifications, and still more difficult to describe them intelligibly. It may even be that the ambivalence displayed in the rela- tions to the parents should be attributed entirely to bisexuality and that it is not, as I have represented above, developed out of identification in conse— quence of rivalry. In my opinion it is advisable in general, and quite especially where neurotics are concerned, to assume the existence of the complete Oedipus complex. Analytic experience then shows that in a number of cases one or the other constituent disap- pears, except for barely distinguishable traces; so that the result is a series with the normal positive Oedipus complex at one end and the inverted nega- tive one at the other, while its intermediate members exhibit the complete form with one or other of its two components preponderating. At the dissolution of the Oedipus complex the four trends of which it consists will group themselves in such a way as to produce a father-identification and a mother-identi- fication. The father-identification will preserve the object-relation to the mother which belonged to the positive complex and will at the same time replace the object—relation to the father which belonged to the inverted complex: and the same will be true, mutatis mutandis, of the mother—identification. The relative intensity of the two identifications in any individual will reflect the preponderance in him of one or other of the two sexual dispositions. The broad general outcome of the sexual phase domi- nated by the Oedipus complex may, therefore, be taken to be the forming of a precipitate in the ego, consisting of these two identifications in some way united with each other. This modification of the ego retains its special posi- tion; it confronts the other contents of the ego as an ego ideal or super-ego. The super-ego is, however, not simply a residue of the earliest object—choices of the id; it also repre— sents an energetic reaction-formation against those THE DEATH OF CERTAINTYI SCIENCE AND WAR choices. Its relation to the ego is not exhausted by the precept: ”You ought to be like this (like your father).” It also comprises the prohibition: ”You may not be like this (like your father)——that is, you may not do all that he does; some things are his prerogative.” This double aspect of the ego ideal derives from the fact that the ego ideal had the task of repressing the Oedipus complex; indeed, it is to that revolutionary event that it owes its existence. Clearly the repression of the Oedipus complex was no easy task. The child’s parents, and especially his father, were perceived as the obstacle to a realization of his Oedipus wishes; so his infantile ego fortified itself for the carrying out of the repression by erecting this same obstacle within itself. It borrowed strength to do this, so to speak, from the father, and this loan was an extraordinarily momentous act. The super-ego retains the character of the father, while the more powerful the Oedipus complex was and the more rapidly it succumbed to repression (under the influence of authority, religious teaching, schooling and reading), the stricter will be the domination of the super-ego over the ego later on—in the form of conscience or perhaps of an unconscious sense of guilt. I shall presently bring forward a suggestion about the source of its power to dominate in this way—the source, that is, of its corn- pulsive character which manifests itself in the form of a categorical imperative. 9.1 Gregor Mendel, Experiments in Plant Hybridisation Gregor Iohann Mendel (1822—84) was the son of Silesian peasants. He got his education as many poor but bright boys did by going to a monastery school. He later joined the Augustinian Order at Brilnn and went on to study at Vienna University, eventually becoming a monk in Moravia (the modern Czech Republic). He began his painstaking work on plant heredity around 1856. By the time he finished his research, setting it aside when he became abbot in 1868, he had bred and examined more than 28,000 pea plants. His evaluation of heredity was ignored for many years since it was both complex and seemed to be more related to hor— ticulture than evolutionary biology. This selection covers his pea plant experiments that uncovered the Notes ' ’ binary system of dominant and recessive genes. 1 1e, the ego is ultimately derived from bodily sensa- tions, chiefly from those springing from the surface of the body. It may thus be regarded as a mental pro- jection of the surface of the body, besides, as we have seen above, representing the superficies of the mental apparatus. [This footnote first appeared in the English translation of 1927, in which it was described as having been authorized by Freud. It does not appear in the German editions] 2 Except that I seem to have been mistaken in ascribing the function of "reality-testing” to the super-ego—a point which needs correction. 3 In order to simplify my presentation I shall discuss only identification with the father. 1. INTRODUCTORY REMARKS Experience of artificial fertilisation, such as is effected with ornamental plants in order to obtain new variations in colour, has led to the experiments which will here be discussed The striking regularity with which the same forms reappeared whenever fertilisation took place between the same species induced further experiments to be Lutdertaken, the object of which was to follow tip the developments of the hybrids in their progeny. 9t$>t Those who survey the work done in this department Wlll arrive at the conviction that among all the 9 ENTERING THE ATOMIC AGE at numerous experiments made, not one has been carried out to such an extent and in such a way as to make it possible to determine the number of differ- ent forms Lmder which the offspring of hybrids appear, or to arrange these forms with certainty according to their separate generations, or definitely to ascertain their statistical relations. It requires indeed some courage to undertake a labour of such far-reaching extent; this appears, however, to be the only right way by which we can finally reach the solution of a question the impor- tance of which cannot be overestimated in connec- tion with the history of the evolution of organic forms. The paper now presented records the results of such a detailed experiment. This experiment was practically confined to a small plant group, and is now, after eight years’ pursuit, concluded in all essentials. Whether the plan upon which the separate experiments were conducted and carried out was the best suited to attain the de— sired end is left to the friendly decision of the reader. 2. SELECTION or THE EXPERIMENTAL PLANTS The value and utility of any experiment are deter- mined by the fitness of the material to the purpose for which it is used, and thus in the case before us it cannot be immaterial what plants are subjected to experiment and in what manner such experiments are conducted. The selection of the plant group which shall serve for experiments of this kind must be made with all possible care if it be desired to avoid from the outset every risk of questionable results. The experimental plants must necessarily—- 349 350 ENTERING THE ATOMIC AGE 1. Possess constant differentiating characters. 2. The hybrids of such plants must, during the flowering period, be protected from the influence of all foreign pollen, or be easily capable of such protection. The hybrids and their offspring should suffer no marked disturbance in their fertility in the successive generations. 3. DIVISION AND ARRANGEMENT OF THE EXPERIMENTS If two plants which differ constantly in one or several characters be crossed, numerous experi— ments have demonstrated that the common charac- ters are transmitted unchanged to the hybrids and their progeny; but each pair of differentiating char- acters, on the other hand, unite in the hybrid to form a new character, which in the progeny of the hybrid is usually variable. The object of the experiment was to observe these variations in the case of each pair of differentiating characters, and to deduce the law according to which they appear in the successive generations. The experiment resolves itself therefore into just as many separate experiments as there are constantly differentiating characters presented in the experimental plants. The various forms of Peas selected for crossing showed differences in the length and colour of the stern; in the size and form of the leaves; in the posi— tion, colour, and size of the flowers; in the length of the flower stalk; in the colour, form, and size of the pods; in the form and size of the seeds; and in the colour of the seed-coats and of the albumen [cotyle- dons]. Some of the characters noted do not permit of a sharp and certain separation, since the difference is of a ”more or less” nature, which is often difficult to define. Such characters could not be utilised for the separate experiments; these could only be applied to characters which stand out clearly and definitely in the plants. Lastly, the result must show whether they, in their entirety, observe a regular behaviour in their hybrid unions, and whether from these facts any conclusion can be come to regarding those characters which possess a subordinate signif~ icance in the type. The characters which were selected for experi- ment relate: 1. To the difiference in the form of the ripe seeds. These are either round or roundish, the depressions, if any, occur on the surface, being always only shallow; or they are ir- regularly angular and deeply wrinkled (P. quadratzmz). . To the difi‘erence in the colour of the seed albumen [endosperm]. The albumen of the ripe seeds is either pale yellow, bright yellow and orange coloured, or it possesses a more or less intense green tint. This difference of colour is easily seen in the seeds as their coats are transparent. . To the dz‘fi‘erence in the colour of the seed—cont. This is either white, with which character white flowers are constantly correlated; or it is grey, grey-brown, leather—brown, with or without violet spotting, in which case the colour of the standards is violet, that of the wings purple, and the stern in the axils of the leaves is of a reddish tint. The grey seed—coats become dark brown in boiling water. . To the difl‘erence in the form of the ripe pods. These are either simply inflated, not con- tracted in places; or they are deeply con- stricted between the seeds and more or less wrinkled (P. sacchomtum). . To the dlfiference in the colour of the unripe pods. They are either light to dark green, or vividly yellow, in which colouring the stalks, leaf- Veins, and calyx participate.1 . To the dzfi‘erence in the position of the flowers. They are either axial, that is, distributed along the main stem; or they are terminal, that is, bunched at the top of the stem and arranged almost in a false umbel; in this case the upper part of the stem is more or less widened in section (P. umbellatum). . To the dzfirerence in the length of the stem. The length of the stem is very various in some forms; it is, however, a constant character for each, in so far that healthy plants, grown in the same soil, are only subject to unimportant variations in this character. GREGOR MENDEL, EXPERIMENTS IN PLANT HYBRIDISATION Ist trial [experiment] 60 fertilisations on 15 plants. 2nd ” 58 n ,, 10 n 3:: “ 35 n ,, io ,, 4th ” 40 n ” ID I) gill! ” 23 u ” 5 n n 34 n g, 10 I) 7th ” 37 n n 10 H :9 a 4- 4. [F1] THE FORMS OF THE HYBRIDS Experiments which in previous years were made With ornamental plants have already afforded evi~ dence that the hybrids, as a rule, are not exactly intermediate between the parental species. With some of the more striking characters, those, for instance, which relate to the form and size of the leaves, the pubescence of the several parts, etc., the intermediate, indeed, is nearly always to be seen" in other cases, however, one of the two parental characters is so preponderant that it is difficult, or quite impossible, to detect the other in the hybrid. This is precisely the case with the Pea hybrids. In the case of each of the seven crosses the hybrid- character resembles that of one of the parental forms so closely that the other either escapes observation completely or cannot be detected with certainty. This Circumstance is of great importance in the determi- nation and classification of the forms under which the offspring of the hybrids appear. Henceforth in this paper those characters which are transmitted entire, or almost unchanged in the hybridisation and therefore in themselves constitute the characters of the hybrid, are termed the dominant, and those which become latent in the process recessive. The expression ”recessive" has been chosen because the characters thereby designated withdraw or entirely disappear in the hybrids, but nevertheless reappear unchanged in their progeny, as will be demonstrated later on. It was furthermore shown by the whole of the experiments that it is perfectly immaterial whether the dominant character belongs to the seed plant or to the pollen plant; the form of the hybrid remains 351 identical in both cases. This interesting fact was also emphasised by Garmer, with the remark that even the most practised expert is not in a position to deter— mine in a hybrid which of the two parental species was the seed or the pollen plant. Of the differentiating characters which were used in the experiments the following are dominant: 1. The round or rormdish form of the seed with or without shallow depression. 2. The yellow colouring of the seed albumen [cotyledons]. 3. The grey, grey—brown, or leather-brown colour of the seed—coat, in association with Violet-red blossoms and reddish spots in the leaf axils. 4. The simply inflated form of the pod. 5. The green colouring of the unripe pod in assoc1ation with the same colour in the stems, the leaf-veins and the calyx. 6. The distribution of the flowers along the stem. 7. The greater length of stem. With regard to this last character it must be stated that the longer of the two parental stems is usually exceeded by the hybrid, a fact which is possibly only attributable to the greater luxuriance which appears in all parts of plants when stems of very different length are crossed. Thus, for instance, in repeated experiments, stems of 1 ft. and 6 ft. in length yielded Without exception hybrids which varied in length between 6ft. and 7 1/E ft. The hybrid seeds in the experiments with seed- coat are often more spotted, and the spots sometimes coalesce into small bluish-Violet patches. The spot- ting also frequently appears even when it is absent as a parental character. The hybrid forms of the seed—shape and the albumen [colour] are developed immediately after the artificial fertilisation by the mere influence of foreign pollen. They can, therefore, be observed even in the first year of experiment, whilst all the other characters naturally only appear in the following year in such plants as have been raised from the crossed seed. 35,, ENTERING THE 5. [F2] THE FIRST GENERATION [BRED] FROM THE HYBRIDS In this generation there reappear, together with the dominant characters, also the recessive ones with their peculiarities fully developed, and this occurs in the definitely expressed average proportion of three to one, so that among each four plants of this gener- ation three display the dominant character and one the recessive. This relates without exception to all the characters which were investigated in the experi— ments. The angular wrinkled form of the seed, the green colour of the albumen, the white colour of the seed—coats and the flowers, the constrictions of the pods, the yellow colour of the unripe pod, of the stalk, of the calyx, and of the leaf venation, the umbel—like form of the inflorescence, and the dwarfed stem, all reappear in the numerical propor- tion given, without any essential alteration. Transi- tional forms were not observed in any experiment. «La-x- These two experiments are important for the deter— mination of the average ratios, because with a smaller number of experimental plants they show that very considerable fluctuations may occur. In counting the seeds, also, especially in Expt. 2, some care is requisite, since in some of the seeds of many plants the green colour of the albumen is less devel- oped, and at first may be easily overlooked. The cause of this partial disappearance of the green colouring has no connection with the hybrid-Charac- ter of the plants, as it likewise occurs in the parental variety. This peculiarity [bleaching] is also confined to the individual and is not inherited by the Off- spring. In luxuriant plants this appearance was fre- quently noted. Seeds which are damaged by insects during their development often vary in colour and form, but with a little practice in sorting, errors are easily avoided. It is almost superfluous to mention that the pods must remain on the plants until they are thoroughly ripened and have become dried, since it is only then that the shape and colour of the seeds are fully developed. Expt. 3. Colour of the seed-coats—Among 929 plants, 705 bore violet-red flowers and grey—brown seed—coats; 224 had white flowers and white seed— coats, giving the proportion 3.15 to 1. ATOMIC AGE Expt. 4. Form of pods of 1181 plants 882 had them simply inflated, and in 299 they were con- stricted. Resulting ratio, 2.95 to 1. Expt. 5. Colour of the unripe pods—The number of trial [experimental] plants was 580, of which 428 had green pods and 152 yellow ones. Con- sequently these stand in the ratio 2.82 to 1. Expt. 6. Position of flowers—Among 858 cases 651 had inflorescences axial and 207 terminal. Ratio, 3.14 to 1. Expt. 7. Length of stem—~Out of 1064 plants, in 787 cases the stem was long, and in 277 short. Hence a mutual ratio of 2.84 to 1. In this experiment the dwarfed plants were carefully lifted and transferred to a special bed. This precaution was necessary, as otherwise they would have perished through being overgrown by their tall relatives. Even in their quite yormg state they can be easily picked out by their compact growth and thick dark-green foliage. If now the results of the whole Of the experi- ments be brought together, there is found, as between the number of forms with the dominant and recessive characters, an average ratio of 2.98 to 1, or 3 to 1. The dominant character can have here a double signification—viz. that of a parental character, or a hybrid-character. In which of the two significations it appears in each separate case can only be deter- mined by the following generation. As a parental character it must pass over unchanged to the whole of the offspring as a hybrid-character, on the other hand, it must maintain the same behaviour as in the first generation [F2]. 6. [F3] THE SECOND GENERATION [BRED] FROM THE HYBRIDS Those forms which in the first generation [P2] exhibit the recessive character do not further vary in the second generation [F3] as regards this character; they remain constant in their offspring. It is otherwise with those which possess the dominant character in the first generation [bred from the hybrids]. Of these two—thirds yield offspring which display the dominant and recessive characters in the proportion of 3 to 1, and thereby show exactly the same ratio as the hybrid forms, while only one— third remains with the dominant character constant. Generation GREGOR MENDEL, EXPERIMENTS IN PLANT HYBRIDISATION The ratio of 3 to 1, in accordance with which the dis— tribution Of the dominant and recessive characters results in the first generatio...
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