C. D. Darlington
Articles written in Journal of Genetics
Volume 16 Issue 2 January 1926 pp 237-251
The chromosome types of three species,
The condition of the constrictions in the three species was followed at different stages: certain constrictions are permanent, others appear at one stage but may be suppressed at another. The phenomenon seems to be the result of a local discontinuity which occurs in different chromosomes at different positions—bisecting the chromosome or cutting off a minute element, which will form, in the contracted state, a “satellite.” Reasons have been shown for believing that the responsiveness in the chromosome to the attraction of the poles is more diffuse than is usually imagined and that this zone of response need not coincide with a constriction.
The appearance of the constriction in all cases may be accounted for by supposing that two chromosome elements are joined by a fine single, or double, chromatin thread surrounded, no doubt, by the film-coat that envelopes the whole chromosome.
Secondary splitting of the chromosomes in the first microspore division was noticed at all stages in
Counts have been made of chromosome numbers in the pollen grains of triploid Hyacinths: various theoretical explanations of the proportions in which they occur have been tested and the results have been found to agree closely with the assumption that each of the extra chromosomes undergoes a constant chance of loss, of the order of one-tenth. The occurrence of somatic variations in chromosome number was noted in heteroploid varieties of
Volume 19 Issue 2 January 1928 pp 213-256
Volume 21 Issue 1 April 1929 pp 1-15
The pollen mother-cell divisions in triploid tulips are described. At prophase only pairs of homologous chromosomes associate at any particular point, but different pairs associate at different points. The fact that three threads lie side by side proves that each corresponds to a whole chromosome rather than to half a chromosome; the parasynaptic interpretation is thus substantiated.
After the formation of diplotene chiasmata, either all three corresponding chromosomes are left attached as trivalents, or one may come to lie entirely free.
Variation occurs in the number of trivalents at the first metaphase, and in the number of chiasmata joining the associated chromosomes.
The association of the chromosomes agrees with the stated requirements of the chromosome theory if we regard the genetical evidence from
It is suggested that the two distinct stages of prophase are, first, that in which attraction exists between four threads, and, secondly, that in which attraction exists between only two of these threads.
Volume 21 Issue 1 April 1929 pp 17-56
Volume 21 Issue 2 August 1929 pp 161-168
A new type of variegation, in
Local differences in the breeding behaviour of the plant are attributed to (i) maternal influence and (ii) failure of embryos of various genetical constitutions under unsuitable maternal conditions.
The inheritance of the dwarf, blotchless and fawn-blotched characters is described.
Volume 21 Issue 2 August 1929 pp 207-286
Volume 22 Issue 1 April 1930 pp 1-14
At diplotene in the prophase of meiosis chiasrnata are not formed at random but with a greater frequency in the neighbourhood of the attachment constriction. The two chromosome types are therefore distinguishable at this stage by the distribution of their chiasmata.
There is no definite change in the relationships of the chromatids (
The great contraction of the chromosomes conceals the details of their relationships, at least in polar views of metaphase, but it has been possible to make a small statistical study of the frequency of chiasmata from side views (see Table I). This, and the separation at anaphase, corroborate the chiasma interpretation of the structure of the bivalent chromosomes at metaphase.
It follows that chromosome behaviour at meiosis must be examined in relation to the possibility of differential frequency of chiasmata as well as of their movement after formation. A knowledge of both these circumstances is necessary before one can consider the analogy with crossing-over results in a particular species.
In the related species
The bearing of this work on the
Volume 22 Issue 1 April 1930 pp 65-93
Volume 22 Issue 2 May 1930 pp 129-151
The basic chromosome number in
The somatic chromosomes in “diploid”
Multiple association occurs amongst the chromosomes of “diploid”
In “triploid” varieties of
Instead of giving a binomial frequency or the elimination of intermediate numbers, natural seedlings of “triploid” apples most frequently have numbers of chromosomes approximately to 2
Thus the pairing, morphology, and breeding results show, directly or indirectly, that the thirty-four chromosomes in the “diploid”
The number seventeen is therefore a secondary (unbalanced) basic number, and the derived series of polyploids (2
The establishment of a secondary basic number must mean (on the analogy of all experimental observations) a definite evolutionary step. It is therefore plausible that the
Volume 24 Issue 1 February 1931 pp 1- Erratum
Volume 24 Issue 1 February 1931 pp 65-96
Volume 24 Issue 3 July 1931 pp 405-474
Volume 28 Issue 2 December 1933 pp 327-328
The sweet cherries (
Volume 29 Issue 2 July 1934 pp 159-173
1. The determination of the relationship of crossing-over to chiasmata and of chiasmata to segregation has made it possible to define the conditions of variation of pairing chromosomes in complex-heterozygotes and sex-heterozygotes and to analyse their behaviour in genetic terms. The object of the present studies is, first, to test the predictions made with regard to sex-chromosomes deducing their genetic structure from cytological observations and, secondly, to note those respects in which the behaviour of the sex-chromosomes throws light on the problems of chromosome mechanics.
2. The sex-chromosomes of the Norway rat each consist of a pairing segment and a differential non-pairing segment. The pairing segment includes the spindle attachment and chiasmata may be formed on one or both sides of it so that the first division is either reductional or equational for the differential segments (Text-fig. 17).
3. The differential segments will have complete sex-linkage, the pairing segments will have partial sex-linkage diminishing in proportion to the crossing-over distance from the differential segments.
4. The shape, movements, and staining capacity of the sex-chromosomes in the rat and elsewhere agree in suggesting that they have a lower surface charge than the autosomes, and this is held to be responsible for the special mechanism of
Volume 31 Issue 2 August 1935 pp 185-212
Volume 32 Issue 2 April 1936 pp 343-352
The simplest method of origin of ring formation, direct segmental interchange, gives interchange heterozygotes which inevitably contain segments of chromosomes of three different types in respect of crossing-over;
This type of reproduction is an example of a compromise between the advantages of free combination and of absolute linkage found in simple sexual reproduction and in clonal reproduction respectively. This compromise is found very widely in plants and animals, although expressed in many different ways. Wherever it occurs it is a means of species formation.
Volume 33 Issue 3 December 1936 pp 465-500
Volume 35 Issue 1 October 1937 pp 97-128
Volume 35 Issue 2 November 1937 pp 259-280
1. Fragments pair with major chromosomes in
2. Less contracted chromosomes in mutant cells have more coils. Spiralization therefore consists in reducing the number of coils.
3. Interlocked chromosomes, like multivalents, may have linear, twisted, or discordant orientations according to the method of interlocking.
4. The type of distribution of the bivalents on the metaphase plate in
5. The central chromosomes of the metaphase plate are pushed to the edge of the group during anaphase in some forms and species. This change may take place asymmetrically both at mitosis and meiosis. It shows that the repulsion from the poles is still acting on the chromosomes while they are moving towards the poles. Thus the anaphase in some forms comes to correspond with the hollow metaphase in others.
Volume 37 Issue 2 February 1939 pp 341-364
Volume 39 Issue 1 November 1939 pp 101-137
Volume 39 Issue 2 January 1940 pp 351-361
Following misdivision of the centromere at meiosis in diploid and triploid
The misdivision and the origin of the iso-chromosome are each likely to be important as affecting the genetic structure of the chromosome and the mechanical properties of the centromere.
Volume 40 Issue 1-2 May 1940 pp 185-213
Volume 41 Issue 1 October 1940 pp 35-48
Volume 41 Issue 1 October 1940 pp 49-64
1. The frequency of chiasmata and of univalents is similar in pollen and embryo sac mother cells of
2. Cells with fewest chiasmata have those chiasmata most strongly localized either proximally or distally.
3. Hence pairing must have begun either near the centromere or near an end. The contact point is optional.
6. Samples of cells used for the study of meiosis in species and crosses must therefore be regarded as representing cross-sections of the process of pairing secured by a variable interruption of the process. Statistical treatment can be used to indicate the order of pairing and the means of interruption.
Volume 41 Issue 2-3 January 1941 pp 275-296
Volume 41 Issue 2-3 January 1941 pp 297-338
Volume 46 Issue 1 April 1944 pp 52-61
Volume 46 Issue 2-3 January 1945 pp 180-267
Irradiation affects the time scale of development by which we measure its effects in the breakage of chromosomes. This explains why single-time comparisons have hitherto shown discordant results. Our comparative breakage-time series enable us to measure both effects and to show direct proportionality of dose and breakage in the pollen grain.
Comparison of pollen grains and pollen tubes shows that their chromosomes have a similar breakability and also inherent rejoinability (as deduced from the frequencies of minutes). But actual rejoining, as between different chromosomes or chromosome arms, such as is revealed in the empirical coefficient of reunion, is frustrated by the close packing of the nucleus.
The pollen-tube nuclei show extreme overlapping of B′ and B″ owing to extreme divergence in rates of nuclear development. They also show a greater primary effect with greater stickiness than in the pollen and (perhaps correlated with this) SR of unbroken ends, which overlaps with the regular SR of broken ends. The general result agrees with that inferred from progeny tests after X-raying
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