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The Chromosomes

Their Numbers and General Importance

by jvind Winge [Comments in square brackets and italics by DRF unless otherwise stated]


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Comptes Rendus des Travaux du Laboratoire Carlsberg (1917) 13, 131-275. Based on Winge's doctoral thesis.

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Following an Introduction (pp. 131-134), Winge's paper is divided into eight chapters, and concludes with a Summary (pp. 264-266):

1. Alternation of generations and nuclear morphology (pp. 135-152).(Click Here)

2. The system of chromosome values in the vegetable kingdom (pp. 152-172)

3. Some new chromosome numbers (pp. 172-191)

4. Theoretical studies on the origin of chromosome numbers (pp. 192-206).(Click Here)

5. Heterochromosomes (pp. 206-219)(Click Here)

6. Persistency of chromosomes, and their heredity significance (pp. 220-238).(Click Here)

7. Chromosomes in hybrid organisms (pp. 239-253)(Click Here)

8. Heterochromatic cells (pp. 235-263)


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What this paper does not do

Winge does not cite "authorities" directly, but notes (p. 131):

"certain authorities on heredity [?William Bateson, ?Wilhelm Johannsen] themselves oppose the tendency to allow the chromosomes a too direct importance in this respect: i.e. as the seat of genetic disposition."

Furthermore Winge fails fully to recognize the role chromosomes can play in sex determination, noting (p. 208) that:

"the number of those who still adhere to the idea as to the existence of sex-determinative chromosomes is steadily decreasing, and from our present standpoint we may maintain that it is not the heterochromosome which is the primus motor in sexual differentiation, though it may, in several cases, more particularly in insects, be associated with one of the other sex, chiefly the female. It is thus rather a question of correlation between the appearance of the chromosome set and physiological or other conditions which determine the sex of the organism (the "Index hypothesis" of Hcker)." 

What this paper does do

However, Winge splendidly summarizes and explores the implications of the pairing of homologous chromosomes in meiosis. This will be summarized on this web page, in the form of quotations from the relevant chapters.


Just to remind you, there is first a modern figure (by DRF) showing (A) normal mitosis (cell division in somatic cells), (B) normal meiosis (cell division, including the reduction division, in gamete-forming cells). The organism is a hybrid between gametes from the father (paternal) and mother (maternal). Since meiosis is normal, the hybrid is fertile.

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Note that in normal meiosis, maternal and paternal chromosomes are "in harmony" and can pair. This permits meiosis to continue, gametes are formed, and so the organism is fertile.


We can also note that as early as 1893, Johann Friedrich Miescher (1844-95), the discoverer of nucleic acid in gametes and elsewhere, suggested that sex may have arisen to correct structural defects in molecules:

"To me the key to the problem of sexual reproduction is to be found in the field of stereochemistry. The 'gemmules' of Darwin's pangenesis are no other than the numerous asymmetrical carbon atoms of organic substances. As a result of minute causes and external conditions these carbon atoms suffer positional changes and thus gradually produce structural defects. Sexuality is an arrangement for the correction of these unavoidable stereometric architectural defects in the structure of organized substances. Left handed coils are corrected by right-handed coils, and the equilibrium restored."

Olby, R. & Posner, E. (1967) An early reference on genetic coding. Nature 215, 556.

Donald Forsdyke circa 2000 

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Why Sex?malefema.gif (1609 bytes)

In Chapter 1 Winge notes that " alternation of generations " between " gametophytic " (haploid) and " sporophytic " (diploid) phases is widespread both in animals and plants. Our gametes (one "generation") are haploid and we (the alternate generation) are diploid. The two generations eternally cycle between the two phases. In some forms of life the haploid phase is of longest duration. When Winge refers to an "individual" he often means the organism in this "original form" in the haploid phase of its life cycle (pp. 142-143):

"That the periodic reversion to the original form -- however brief it may be -- is of great importance for plants and animals will doubtless be generally admitted, and we may in the following, presupposing the gametophyte to be the original organism, consider what advantages may be thought to accrue to the living form thereby... Presuming then, that unicellular organisms even in the past at times propagated sexually, much as such organisms now do, we have to consider what advantages even a brief fusion of two individuals could have had for their further existence."

He then extends earlier work of Galton, Butler, Weismann and Montgomery to suggest what we might now refer to as the correction of genetic errors. Winge begins with the simple idea of complementation (pp. 143-145):

"It is now reasonable to suppose that two individuals on fusing together would to a certain degree be able to replace what might be lacking in each; it seems at any rate likely that the zygote, as a product of two individuals, may be regarded as better adapted to its surrounding than either of the two whence it was derived. After fertilization [and development], separation [meiosis] takes place, and we then presume that both individuals [gametes] would as a rule have derived some benefit from the temporary union, inasmuch as they will have been able to some degree to help out each others shortcomings. ... A continually repeated intermingling of individuals during the diplophase will afford the greatest likelihood that the species may retain the substantial elements which determine the entire nature of the organism. An individual failing in a (gametophytic) individual may be repaired in its subsequent fusion with another, so that the gametophytes again formed by the double organism [that's you and me] leave the diplophase in better condition than prior to fertilization. The essential importance of fertilization would thus be, that it enables individuals, especially the gametophytes, to supplement each other... Albeit the higher plant and animal individuals really are of a double nature, they nevertheless appear and act as harmonious units, and the dualism is, from a morphological point of view, rarely observed...[e.g.] with the small snail Crepidula, ... the two nuclei [paternal and maternal] are separate throughout most of the animal's life."

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Polyploidy and Chromosome Pairing

In Chapter 4 Winge examines fertile and unfertile (sterile, apogamous) polyploids, and the pairing of chromosomes, which reveals some "fundamental principle":

"It will be here necessary to go further into the peculiarities of the chromosomes themselves. The most characteristic feature of these is ... their tendency to occur in pairs. Chromosomes are frequently found paired in the somatic cells, and [are] continually [paired] in the gonokonts [gamete-forming cells], the parent chromosomes exhibiting a mutual affinity.... Chromosomes, once separated, unite in pairs. This evidently reveals some fundamental principle in the nature of chromosomes, and must be connected with the dualism to which every sporophyte [diploid] owes its origin."

The degree of genetic relatedness between two individuals critically affects the pairing of their chromosomes in the hybrid which results from a merging of their gametes:

"Generally speaking, only nearly related plants are capable of interfertilization and the production of progeny able to live on [i.e. of producing hybrid progeny which are not sterile]; it is therefore certain that only such gametes as harmonize physiologically -- or better, perhaps, physiogenetically -- can enter into the formation of a duality such as the sporophytic [diploid] organism. The gametophytic [haploid] cell can rightly be considered as one harmonic whole, and we may further presume that only physiogenetically uniform nuclei -- and especially their chromosomes -- are able to affect each other. It will indeed doubtless be only reasonable to suppose that the greater or lesser degree of physiogenetic similarity or harmony will determine what common result is to arise from the union of two gametes."

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A modern rendition of Winge's hypothesis that polyploidy "cures" hybrid sterility. In the hybrid between two diploid parents (A) the chromosomes from the mother (white) are not "in harmony" with the chromosomes from the father (black), so pairing fails, and no gametes are produced. 

     When the same chromosomes are duplicated to make tetraploid parents (B), pairing succeeds because, although white (maternal) is still incompatible with black (paternal), there is still a pairing partner (white with white, and black with black). The resulting gametes are diploid, and will unite with a similar diploid to generate another tetraploid organism. 

     The cause of the hybrid sterility in (A) is "chromosomal". However, pairing and many other aspects of gametogenesis require gene products. If one of these gene products is defective then hybrid sterility ("genic") may result, but this time it will not be "cured" in the tetraploid (see Dobzhansky, 1937. Genetics and the Origin of Species. Columbia University Press).

Donald Forsdyke

Winge next offers a classification depending on the "physiogenetic likeness between gametes", a fundamental characteristic determining the number and type of barriers between them:

  • (i) no barriers (philozygoty)

  • (ii) post-zygotic developmental, or chromosome pairing, barriers (pathozygoty)

  • (iii) prezygotic barriers (misozygoty)

"1. Philozygoty ["denotes the highest degree of harmony between the sexual cells of two organisms"]... for instance two gametes from the same species of plant. Philozygoty must thus be said normally to characterize gametes belonging to one and the same systematic species [as defined on morphological grounds by biologists]. We may, however, also find that gametes derived from different [again as defined by systematists] species or forms ["heterogamous" as opposed to "homogamous"] have a harmonizing or corresponding "inner physiology" i.e. possess the qualities requisite for a pairing between their chromosomes, and thus the formation of a harmonic common product, a zygote with unimpaired vitality. Heterogamous organisms may thus also be philozygotic. As in the case of homogamous organisms, so also here the parent chromosomes are united in pairs -- at any rate in the gonotokont [gamete forming cell] nuclei, after which they again separate, the two sets of parent chromosomes being distributed on the daughter cells [to become gametes] during reduction division.

2, Pathozygoty. By this I mean ... that two gametes may enter into the formation of a common zygote [i.e. no prezygotic barrier], which, however, owing to the less marked harmony between the constitution of the gametes, may often be only partly capable of development, or not capable of development in the normal manner [hybrid inviability or sterility]. This category will only include gametes derived from different species or races, i.e. heterogamous gametes. When such heterogamous gametes unite, one of the following alternatives must take place:

A. Direct union of the chromosomes. If the parent chromosomes, in accordance with the nature of chromosomes in affinity, pair directly, we must presume that this will ... give rise to a zygote which may either be apogamous [sterile], or normally sexed [fertile].

(a) Apogamous [sterile] forms. On the fusion of heterogametes [gametes from different species], a zygote will be formed having the sum of the chromosome number in the gametes. When the chromosome numbers of the parents are different, the pairing will ... be incomplete, but when the chromosome numbers are alike, a complete union of homologous chromosomes will take place. In both cases then, we have an apogamous [sterile] zygote, and as the related species in a genus usually have the same chromosome number, x, the apogamous zygote will in most cases have 2x chromosomes. Apogamous species with normal chromosome number (compared with the remaining species of the genus) are also ... found in nature.... From the synapsis stage, where the separation of parent chromosomes is prepared, irregularities occur, so that reduction cannot take place, ....

(b) Normally sexed [fertile] forms. There is also the further possibility that the chromosomes meeting in the zygote may all, or some of them only, constitute a new chromosome set, when the zygote will thereafter represent something entirely new; a new species with a set of chromosomes rendered stable for the future, and normally sexed [fertile]. It seems to me ... natural to suppose ... that the homologous or most closely harmonizing elements in the nuclei of the gametes continually seek out each other in order to form harmonious unions, just as -- to use a purely illustrative comparison -- in chemistry, atoms of greatest mutual affinity constantly tend to unite.

B. Indirect chromosome union [Polyploidy]. Where a less-marked harmony exists, we must then suppose that this will be visibly expressed by the fact that the chromosomes derived from the two gametes will not unite in pairs at all, but distribute themselves throughout the primary cell of the zygote, as if no dualistic relation of any kind existed. If the chromosomes are to find a partner, then each of the chromosomes in the zygote must divide [thus creating a potential pairing partner], for thus indirectly to produce [the potential for] a union of chromosomes, and we must assume that this is realized in the hybrid zygotes which have any possibility of propagating -- in accordance with what we know from experience as to the behaviour of pairs of chromosomes. The hybrid sporophyte thus produced will then have 4x chromosomes, taking the number from the parent gametes as x.

     After this, either the chromosome pairs will have the power of further separating by reduction division, transmitting one set of the chromosomes from either parent to each of the gametes -- in which case we have a new hybrid organism with the qualities of a pure species and "double" chromosome number [polyploid]; i.e. containing the sum of the chromosome numbers in the parent species. Or, if the power of reduction has been lost, but the power of continued existence [for that generation] otherwise retained, the result will be an apogamous [sterile] species [individual] with 4x chromosomes.... With regard to the apogamous species, the chromosome number here is ... generally just twice that of the related normally sexed species, and as sexual sterility is itself characteristic of many hybrids, I consider it highly probable that apogamous species are derived from crossings between those normally sexed....

C. No chromosome union. Where the mutual harmony between the two united gametes of heterogamous origin is so slight that their relation becomes almost disharmonious, the interaction between the two organisms will in all probability be of briefer duration and of a less intimate character. This might naturally result in the chromosomes of the two gametes failing to unite either directly or indirectly. I believe I am justified in assuming that the chromosomes of sporophytes capable of sexual development must continually act in pairs, and I must accordingly conclude that when neither direct nor indirect union of chromosomes takes place, then the organism is doomed, and can only exist as an embryo -- possibly with the power of cell division, as long as it is nourished by the mother tissues.

3. Misozygoty [prezygotic barrier]. Gametes of systematically widely differing organisms [defined by systematists using morphological criteria] will as a rule altogether lack the power of uniting in a zygote. Not only is there too little similarity between the constitutions of such gametes; there is moreover no harmony between them, and in consequence, nothing calculated to produce the mutual affinity which is inseparable from all fertilization. The term misozygoty then, I use to designate this lack of mutual harmony; a reciprocal disinclination rendering fertilization impossible."

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Hybrid Sterility within Incipient Species

I n Chapter 5 there is discussion of odd, unpaired, "heterochromosomes", which, in some cases are the sex chromosomes. Under the same heading,Winge considers chromosomes in hybrids between members of allied species, where mispairing may result in free chromosomes. Of significance for the conception of incipient species within the parental species we may note Winge's remark:

 "I could imagine that genotypic differences might be present within one and the same species, causing the extreme forms [within the species], on intercrossing, to act very much as do entirely different species -- i.e. to produce offspring in which the parental chromosomes are not normally paired, which again would involve the further consequence that the formation of sexual cells [gametes] must proceed abnormally or even not take place at all [i.e. hybrid sterility within a species, indicative of potential incipient species formation].... The frequent appearance of plant heterochromosomes in sexually abnormal forms is ... a further indication of the correctness of my view as to the importance of chromosome pairing. Future researches must decide whether the "good" species in which heterochromosomes are found should not really be classed as hybrids."

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Effective Pairing Results in Fertility

In Chapter 6 Winge considers the hereditary significance of chromosomes, and the actual chemical basis by which homologs might "repair" each other as a result of meiotic pairing. He notes that:

"there is always a certain interaction taking place between the parent chromosomes in the somatic cells.... Such interplay, which is undoubtedly an indication of dualism in each individual somatic cell, is necessary in all normal reproduction [mitosis]. The pairing need not perhaps always be visible, just as the chromosomes themselves are not always so, but the mutual affinity between the parent chromosomes in pairs is, I opine, present in normal plants."

    Winge acknowledges evidence, often involving transmission by the female, that in some cases "cytoplasmic peculiarities" may be responsible for hereditary transmission:

"A male plant does not contribute the same amount towards fertilization as the female. The egg in higher plants, as also among animals, contains a quantity of cytoplasm, whereas the male gamete is an extremely small organism, the nucleus of which has but very little cytoplasm or none at all."

However, the main carriers of hereditary information are the chromosomes:

"The hereditary differences are not themselves visible; it is not the morphological differences in the chromosomes, but variations of a far more delicate nature, which give rise to the external morphology [of the organism] .... 'Predispositions' in the chromosomes cannot of course be supposed to be present as morphologically demonstrable units, but must rest on some chemical conditions in the chromosomes as lie far beyond the range of our present knowledge."

He then considers in detail the nature of the interaction during chromosome pairing:

"Starting now with two philozygotic gametes, e.g. two gametes belonging to a plant such as Sisymbrium strictissimum, the haploid chromosome number of which is 8, then on fertilization (alien fertilization) [I think Winge mean alien in the sense that the chromosomes are not precisely identical] a germ with 8 + 8 chromosomes in the nucleus will be produced. Each chromosome from the male sexual cell has its partner among those of the egg cell, but the 16 chromosomes remain individualized, although the mutual attraction between the partner chromosomes may occasionally find visible expression during the diplophase [period when cells are diploid] in the form of paired prochromosomes in the somatic cells.

    Not until the gonokonts [gamete-forming cells] are formed -- considering now the pollen mother cells -- do we find in the prosynapsis an intimate parallel conjugation between the chromosomes from the female and those from the male respectively. The importance of this pairing must, I imagine, be that the chromosomes, two by two, supply each other with missing chromatic parts, possibly ides or pangenosomes ([genes]; Strasburger 1906) in case such could have been lost during the ontogenesis [development] of the sporophyte [diploid] -- and which are necessary if the organism (species) is fully to retain its disposition, i.e. to remain genotypically unaltered. That such "loss" must frequently take place, I have already mentioned (p. 143). During the synapsis and subsequent stages,  the chromosomes are again separated, and become once more fully individualized during diakinesis [a stage of meiosis]. The chromosomes have then undergone this alteration: they have to a greater or lesser degree effected an interchange of substances, so that while each in the main still has its original composition, all are, none the less, affected by the temporary pairing in the points where they have individually suffered loss during the ontogenesis of the double organism.

    The chromosomes which are separated after reduction division -- we need here consider only a single pair, A and a -- will thereafter no longer be A and a, but A1a1 and a1A1, -- A1 and a1 indicating, that during ontogenesis a change has taken place in the qualities of the chromosomes, and thus also of the gametes [derived from them], chiefly through loss, while the subindices a1 and A1 indicate the mutual influence exerted during the pairing of the chromosomes.

    We must now assume that the changes which have taken place in the gametes are as a rule extremely slight, the chromosomes passing almost unaltered through the nuclear divisions, the altered formula for the gametes only denoting a change of quality so extremely small that it can as a rule not be demonstrated at all. Theoretically, however, the newly formed gametes are at least at times "impure". Let us consider this point further.

    Taking again two gametophytes belonging to the same species of plant, and considering especially the sexual nuclei, we find that these are, as regards the number of chromosomes, entirely alike, although of different origin. Each chromosome in the male nucleus has a corresponding one [homolog] in the female. The genotypic differences normally present are due solely to differences in the component parts of the chromosomes in the two nuclei. -- It will here suffice to consider a single chromosome in the female nucleus and its homologous fellow in the male, altogether disregarding the segregations which will arise when whole chromosomes are interchanged during reduction division.

     The female chromosome will be characterized, for instance, by the following components:

a b c d e f g h i

and the male by:

a x c d e f g y i

    Only two units are different, b and h in the female nucleus [top] being represented by other units in the male [bottom] , to wit, x and y, whereby the cells become genotypically dissimilar. On fertilization, all that now happens is that the two chromosomes both enter into the germ nucleus; but when the sporophyte has reached the reduction stage, where new gametes are to be formed, something will have been lost during the numerous mitoses, and the homologous chromosomes under consideration will now have a slightly altered appearance [a contradiction since Winge states above that such 'predispositions' may not affect chromosome morphology]. We can here imagine several cases, according as one or another unit has fallen away.

    The male, or the female chromosome respectively, might for instance in the nucleus of a spore mother cell present the following appearance:

a b - d e f g h i
a x c d e f - y i

     Each of the chromosomes has thus lost one unit, c and g respectively, but in the subsequent prosynapsis, the pairing of the chromosomes takes place by parallel conjugation, and I presume then that the two chromosomes will mutually replace what each has lost, the male chromosome [bottom] giving off parts of its c to the female [top], and the latter some of a unit g to the male. Thereafter, the (parent) chromosomes again separate, and will -- as it is seen -- have exactly  the same appearance as when they entered upon the common zygote formation.

     Theoretically, then, the gametes might thus easily become "pure" and the segregation complete. Suppose, however, the appearance of the chromosomes in the spore mother cell to be thus:

a - c d - f g h i
a x c d e f - y i

Then the units e and g can, by mutual replacement, easily be formed again; with b, on the other hand, this is not the case, and the male chromosome does not contain this unit at all. We must therefore presume that the male chromosome [bottom] in prosynapsis will deliver, to the female, material of the corresponding unit x, so that the chromosomes in the diakinesis when anew separated, will have the following composition:

a x c d e f g h i

a x c d e f g y i

     The gametes -- here only the female [top] -- have thus during the sporophytic phase undergone alteration: dispositions have been transferred from one to the other [gene conversion]. The segregation will consequently be impure, though how far it may be possible to discover the fact is another matter. As more or fewer units are lost, a greater or lesser change will have taken place in the gametes, but probably only greater changes, or such as particularly affect the external morphology, will be discernable in practice.

     Finally, we have to consider a third possibility, which may be expressed thus:

a b c - e f g h i

a x c - e f g y i

    The two chromosomes have here lost the same qualities, and units, and are thus unable to replace these. It will then probably depend upon the nature of the dispositions represented by such units [hand waving ?], whether the gametes are capable of continued existence or not.

     My supposition, that the chief importance of fertilization -- or rather, of the alternation of generations -- is the mutual supplementation of the gametes, is, I consider, a very probable one. I can find nothing to prevent the acceptance of such a theory, and believe that the Mendelian laws of segregation and deviations from the same, as well as Johannsen's "pure lines" and other fundamental rules of heredity may well permit, or even support, such a hypothesis.

     I imagine, that as a rule only few and slight "losses" will take place in the course of each gametophytic or sporophytic ontogenesis [development] respectively, so that they will in most cases be fully compensated for during the chromosome conjugation in prosynapsis. Generally therefore, "pure" i.e. unaltered, gametes may be produced after reduction division, viz: the two parent gamete types, and even if some interchange has taken place, there will nevertheless arise chromosome-types corresponding in the main with those of the parent gametes, but -- after the intermingling during the diplophase -- distributed by chance on the gametes....

     As regards the pure lines, we must here of course consider the male and female chromosomes as being altogether alike in structure. On considering a single pair of chromosomes, for instance, it may be characterized, let us say, by the following qualities:

a b c d e f g h i

a b c d e f g h i

     When in the course of ontogenesis [development] certain units are lost by the male [top] chromosome, it will in the subsequent synapsis have these replaced by the female [bottom], and vice-versa. As the gametes are throughout entirely homologous, no new units will ever be transmitted from one to the other during chromosome pairing, but if both chromosomes should lose the same unit, then the zygote produced will be genotypically altered, and will then probably represent what we know as a retrograde mutant...."

   Finally, Winge considers the implications of this for understanding the deleterious effects of close inbreeding, and answers the objection, -- if sex is so beneficial, how come the dandelions are doing so well?

   "That inbreeding can also lead to unfortunate results, as is proved by instances from both animal and vegetable kingdoms, corresponds extremely well with my theory, as the closer relationship between gametes will often naturally preclude the mutual replacement of loss in the chromosomes,which, owing to their common derivation, lack the same units. The ill effects of  inbreeding should thus be due to retrogressive mutations....

     Many plants, however, continue to develop and flourish even when selfpollination constantly takes place through many generations, just as various sexually abnormal individuals, of Taraxacum [dandelion], for instance, thrive excellently by purely vegetative propagation. If such instances be adduced as an argument against my observations on the significance of alternation of generations, I would again point out, as before, that a clone or a definite biotype may possibly retain its qualities for a long time -- especially when selection takes place, and it is perhaps only reasonable, that nature should exert a selection among the manifold "vegetative" individuals, for instance in Taraxacum....

      I cannot admit that the individuality of the chromosomes should necessarily be lost, even though interchange between them may take place in prosynapsis and synapsis. The term "Individuality" is, it is true, difficult to define in this connection, but the cytologists who have demonstrated the individuality of chromosomes, really mean only the 'persistency and retaining of formal peculiarities throughout the generations'. The qualitative consistency -- or individuality -- cannot of course be studied under the microscope. The position might be illustrated, for instance, by pointing out that two ships at sea without losing their "individuality" might well exchange certain wares in order to complete their stores; the chromosomes can doubtless carry on  a similar traffic during their conjugation in the synapsis stage...."

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Defective Pairing Results in Sterility

In Chapter 7 Winge considers chromosome in hybrid organisms which often show partial or complete sterility. The hybrid sterility resulting from "heterogeneous fertilization and all that it involves should be particularly valuable in the study of chromosomes". Like Romanes and Bateson, he draws a distinction between what we now know as "genic" and "chromosomal" causes for hybrid sterility.    

"Among plants, specific hybrids are as a rule sterile; ...On the whole, ... imperfect reduction [at meiosis] is associated with the hybrid nature, but it would be only reasonable to suppose that other causes might affect the stage [the reduction stage] in the alternation of generation which must doubtless be considered as the most delicate.

    That the 'striving' of the hybrid plant to complete the cycle of the alternation of generations may also be stopped at an [even] earlier stage has been shown by Tischler (1906, 1907, 1908) and Janczewsky (1909) who found, in Ribes hybrids, Syringa and Mirabilis, that the tapetum of the anthers became abnormally developed [withered?], so that it was evidently unable to nourish the pollen mother cells. I have, however, found a similar state of things in a monocious individual of Humulus lupulus (Winge 1914) from which it would seem that internal discrepancies of another nature can also produce the same phenomenon.

    The life cycle of sterile hybrids -- both in plants and animals -- appears to be regularly interrupted either at so late a stage as in the above-mentioned instances, i.e. on account of the imperfection of the sexual organs [with respect to gametogenesis; i.e. post-zygotic gonadal barriers] -- or in plants, especially of the spore formation -- or at an extremely early stage, soon after the sporophyte [diploid] has been formed by the hybrid fertilization [post-zygotic developmental barrier], and that there are thus two critical stages. Once the hybrid has passed the first test, which decides whether it is capable of independent vital action at all [hybrid inviability], it developes with often surprising luxuriance [hybrid vigour], until the inadequacy of the sexual products put an end to its further propagation [hybrid sterility], and the biotype produced dies with the individual..."

Winge then considers chromosomal changes occurring in plant and animal hybrids, such as those described by Federley and Guyer (Click Here; although he only cites Guyer's 1900 abstract in Science).

"Federley states that the irregularities in the hybrid first become apparent during reduction division, as in all probability the relation between specifically different chromosomes only then becomes intimate, so that the disharmony finds expression.... In S. austauti X S. populi [ both with the same number of chromosomes] the chromosome number in the spermatocytes varied between 28 and 33, some few chromosomes at times neglecting to conjugate. 

    Federley is now of the opinion that the conjugation of a varying number of chromosomes in the different spermatocytes indicates a qualitative difference, arising in the course of ontogenesis, between the chromosomes in question. Federley is here evidently arguing along the same lines as I have endeavoured to make clear in the foregoing; that nuclear division does not proceed with such precision as to maintain the division product constantly equal to its origin. 

    He follows up his victory [victory because he agrees with Winge?] by asserting that an alteration of chromosome qualities contradicts the theory of the individuality of chromosomes, which demands an identical set of chromosomes in all gametocytes of the first order, and he believes that segregations can thus take place independently of Mendel's laws [deviating from Mendelian predictions].... Federley presumed -- as I did myself -- that the sterility of the offspring is in inverse proportion to the power of conjugation [effective homologous pairing] in the chromosomes...."

C. D. Darlington continued this further in "The behaviour of polyploids" (1927 Nature 119, 390). 

Ojvind Winge was born in May 1886 (the same month as Romanes' Linnean Society lecture on physiological selection), and died in 1964. Bateson met him in the 1920s. Waclaw Szybalski worked with him from 1947-49 (see "My Road to Ojvind Winge, the Father of Yeast Genetics" 2001. Genetics 158, 1-6).

Photographs were kindly reproduced by Dr. Morten Kielland-Brandt from The Carlsberg Laboratory 1876-1976. Edited by H. Holter and K.Max. Moller. Pub. Rhodos, Copenhagen, 1976. Copyright permission was given by Dr. Gunver Kyhn for the Carlsberg Foundation. In the book there is a brief biography by M. Westergaard (see also Compt. Rend. Trav. Lab. Carlsberg 34, 1-24; 1965 (Click Here)

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End Note (Aug 2015): Hybrid Sterility Precedes Whole Genome Duplication

Analysis of genome sequences usually provides evidence for one or more ancient whole genome duplications (WGDs). A WGD that generates polyploidy may occur within one organism (autopolyploidy) or result from the fusion of two independent genomes that, when of closely related (allied)  species, can be referred to as allopolyploidy. With autopolyploidy, differences between the duplicates will accumulate after the fusion event. With allopolyploidy, differences between the two genomes will already exist and there is often hybrid sterility. To these differences will be added further differences that accumulate after the fusion event.

     In an elegant phylogenetic analysis of the genome sequences of various yeast species, Marcet-Houben and Gabaldon (2015; PLOS Biology 13(8):e1002220) were able to distinguish between these possibilities. In agreement with Winge's hypothesis, they found that many differences existed prior to the fusion event. This suggests that WGDs arose in order to "cure" the hybrid sterility that would have resulted. The WGD was of immediate selective advantage since it permitted the line to continue.

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This page was created circa 2000 and last edited 13 Aug 2015 by Donald Forsdyke