THE CHROMOSOMES IN HEREDITY W. S. SUTTON Sutton, W. S. 1903. The chromosomes in heredity. Biological Bulletin, 4:231-251. ESP Electronic Scholarly Publishing http://www.esp.org© 1998, Electronic Scholarly Publishing Project http://www.esp.org This electronic edition is made freely available for educational or scholarly purposes, provided that this copyright notice is included. The manuscript may not be reprinted or redistributed for commercial purposes without permission.© 1998, Electronic Scholarly Publishing Project http://www.esp.org This electronic edition is made freely available for educational or scholarly purposes, provided that this copyright notice is included. The manuscript may not be reprinted or redistributed for commercial purposes without permission. Sutton, W. S. 1903. The chromosomes in heredity. Biological Bulletin, 4:231-251. THE CHROMOSOMES IN HEREDITY W. S. SUTTON IN A RECENT ANNOUNCEMENT of some results of a critical study of the chromosomes in the various cell generations of Brachystola1 the author briefly called attention to a possible relation between the phenomena there described and certain conclusions first drawn from observations on plant hybrids by Gregor Mendel2 in 1865, and recently confirmed by a number of able investigators. Further attention has already been called to the theoretical aspects of the subject in a brief communication by Professor E. B. Wilson.3 The present paper is devoted to a more detailed discussion of these aspects, the speculative character of which may be justified by the attempt to indicate certain lines of work calcu-lated to test the validity of the conclusions drawn. The general concep-tions here advanced were evolved purely from cytological data, before the author had knowledge of the Mendelian principles, and are now presented as the contribution of a cytologist who can make no preten-sions to complete familiarity with the results of experimental studies on heredity. As will appear hereafter, they completely satisfy the condi-tions in typical Mendelian cases, and it seems that many of the known deviations from the Mendelian type may be explained by easily con-ceivable variations from the normal chromosomic processes. It has long been admitted that we must look to the organization of the germ cells for the ultimate determination of hereditary phenomena. Mendel fully appreciated this fact and even instituted special experi-ments to determine the nature of that organization. From them he drew the brilliant conclusion that, while, in the organism, maternal and pa-ternal potentialities are present in the field of each character, the germ cells in respect to each character are pure. Little was then known of the nature of cell division, and Mendel attempted no comparisons in that direction; but to those who in recent years have revived and ex-2 W. S. SUTTON (1903) FOUNDATIONS OF CLASSICAL GENETICS tended his results the probability of a relation between cell organization and cell division has repeatedly occurred. Bateson4 clearly states his impression in this regard in the following words: “It is impossible to be presented with the fact that in Mendelian cases the crossbred produces on an average equal numbers of gametes of each kind, that is to say, a symmetrical result, without suspecting that this fact must correspond with some symmetrical figure of distribution of the gametes in the cell divisions by which they are produced.” Nearly a year ago it became apparent to the author that the high degree of organization in the chromosome–group of the germ cells as shown in Brachystola could scarcely be without definite significance in inheritance, for, as shown in the paper5 already referred to, it had ap-peared that: 1. The chromosome group of the presynaptic germ cells is made up of two equivalent chromosome series, and that strong ground exists for the conclusion that one of these is paternal and the other maternal. 2. The process of synapsis (pseudoreduction) consists in the union in pairs of the homologous members (i.e., those that correspond in size) of the two series.6 3. The first postsynaptic or maturation mitosis is equational and hence results in no chromosomic differentiation. 4. The second postsynaptic division is a reducing division, resulting in the separation of the chromosomes which have conjugated in synapsis, and their relegation to dif-ferent germ cells. 5. The chromosomes retain a morphological individuality throughout the various cell divisions. It is well known that in the eggs of many forms the maternal and paternal chromosome groups remain distinctly independent of each other for a considerable number of cleavage mitoses, and with this fact in mind the author was at first inclined to conclude that in the reducing divisions all the maternal chromosomes must pass to one pole and all the paternal ones to the other, and that the germ cells are thus divided into two categories which might be described as maternal and paternal respectively. But this conception, which is identical with that recently brought forward by Cannon7 was soon seen to be at variance with many well known facts of breeding; thus: 1. If the germ cells of hybrids are of pure descent, no amount of crossbreeding could accomplish more than the condition of a first cross.The Chromosomes in Heredity 3 First published in: Biological Bulletin, 4:231-251 2. If any animal or plant has but two categories of germ cells, there can be only four different combinations in the offspring of a single pair. 3. If either maternal or paternal chromosomes are entirely excluded from every ripe germ cell, an individual cannot receive chromosomes (qualities) from more than one an-cestor in each generation of each of the parental lines of descent, e.g., could not inherit chromosomes (qualities) from both paternal or both maternal grandparents. Moved by these considerations a more careful study was made of the whole division process, including the positions of the chromosomes in the nucleus before division, the origin and formation of the spindle, the relative positions of the chromosomes and the diverging centro-somes, and the point of attachment of the spindle fibers to the chromo-somes. The results gave no evidence in favor of parental purity of the gametic chromatin as a whole. On the contrary, many points were dis-covered which strongly indicate8 that the position of the bivalent chro-mosomes in the equatorial plate of
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