They all contain a liquid, a linin network, and a chromatinthread or network, but they differ most remarkably in details, so that the variety among the nucleii is almost endless (Fig.
The essential object of this complicated phenomena of karyokinesis is to divide the chromatin into equivalent halves, so that the cells resulting from the cell division shall contain an exactly equivalent chromatin content.
This explanation is that some of the chromatin material or germ plasm is handed down from one generation to another, and is stored temporarily in the nucleii of the reproductive cells.
This undifferentiated chromatin material originally possessed powers of producing a new individual, and of course it still possesses these powers, since it has remained dormant without alteration.
This process of the formation of the polar cells is thus simply a device for getting rid of some of the chromatin material in the egg cell, so that it may unite with a second cell without doubling the normal number of chromosomes.
Plainly, we must conclude that the chromatin material is something of extraordinary importance to the cell, and the centrosome is a bit of machinery for controlling its division and thus regulating cell division.
The eggs arise from the other cells of the body, but during their growth the chromatin splits in such a way that the egg contains double the number of chromosomes, i.
This we can only believe to be the result of a differentiation in theirchromatin material.
The chromatinis broken into threads or chromosomes, cr.
Hence, if the number of chromosomes in the next generation is to be kept equal to that in the last generation, this egg cell must get rid of a part of its chromatin material.
All things considered, this chromatin is probably the most remarkable body connected with organic life.
Beginning of division; thechromatin arranged in the form of a long thread.
The four parts of thechromatin arranged symmetrically between the centrosomes and the star-like “spheres.
The chromatin always gives the reaction of an acid, while protoplasm is basic; besides that it seems to be a centre of oxidation.
When speaking of maturation, we mentioned that half of the chromatin was thrown out of the egg by that process: now this half is brought in again, but comes from another individual.
Resting cell; the chromatin distributed in the form of small granules inside the nucleus.
The thread of chromatin cut into four parts, the “chromosomes.
As the bulk of the chromatin remains constant from one cell-generation to another, it must double its bulk between successive divisions.
Moreover, we have no reason for supposing that the division of the chromatinin amitosis is not as meristic, and its subsequent distribution as equal, as is so visibly the case in mitosis.
In other words the chromatin must be regarded as being composed of individual units, each with a definite constant structure and maximum growth (Boveri, 1904).
Concentration of the chromatin has made visible the belated transverse division.
The work of the self-propagating chromatin granules is so ordered that periods of undisturbed metabolic activity alternate with periods of reproductive activity.
This conclusion is strongly suggested, not only by the evidence in favour of the individuality of the chromosomes considered above, but also by the independent reproductive activity of the chromatin granules in the prophase of mitosis.
In this latter type the chromatin of the oocyte, as this prepares for the first maturation division, resolves itself into 12 (instead of 24) longitudinally split chromosomes (fig.
The situation then is that there are two nuclei of the same size and both charged with chromatin of the same general character, in close proximity, and waiting to fuse with each other.
By this division of the chromatin fibers, and their separation from each other to opposite poles of the spindle, two starlike chromatin figures are produced (dyaster).
As the threads stain when coloring agents are applied to them, they are called chromatin fibers, and the loose coil is the chromosome (Waldeyer).
When the cell commences to divide, the meshes of the network of chromatin contract and the centrosome divides into two parts (Fig.
The nucleus of the egg and that of the spermatozoid then begin at the same time to concentrate their chromatin in the form of chromosomes (Fig.
Shortly afterward the particles of chromatin concentrate in the form of convoluted rods called chromosomes (Figs.
In this way the nuclear chromatin of our germinal cells becomes the carrier of all the hereditary qualities of the species (hereditary mneme), and more especially those of our direct ancestors.
At the same time a nuclear liquid arising from the protoplasm of the egg becomes concentrated around the chromatin of the spermatozoid, while the nucleus of the egg remains in place and does not change.
Before this, however, the nucleus of the egg has thrown off a part of its chromatin called a polar body, and it now possesses only half as much chromatin as the other cells of the body of the individual.
The male and female chromatin are colored red and blue respectively.
The celebrated zoölogist, Weismann, considers that thechromatin of each germinal cell contains a considerable quantity of particles each of which is capable of forming an entire organism similar to the parents; these he calls "ides.
It is inevitable that irregularities will occur, and if the original chromatin produced a certain character, who shall say what more or less of that chromatin will produce?
In certain cases there is no evident quantitative difference of chromatin as a whole, but there may in all cases be a difference in the quantity of special sex-chromatin contained in the X element.
If a given character is represented by a portion of the chromatin in the original ovum, this has to be divided so many times, and each time to grow to the same condition as before.
A double quantity of special chromatin may be the cause of the greater anabolism of the ovum.
These results tend to show that factors are not indivisible units, and segregation is rather the difficulty of chromatin or germ plasm from different race uniting together.
The chromatin is strangely broken up into irregular clumps, and probably no two of these degenerate sperm-heads can be found which are alike.
As the chromatin begins to condense for the second mitosis, disintegration of the element x becomes apparent.
Chromatin massed at poles of spindle; element x isolated at one pole.
There is no resting stage, but the new spindle is formed from the remains of the old one, and the spindle-shaped mass of chromatin seen in figure 188 either passes into the center of the new spindle or becomes enveloped by it.
Figure 149 is an exceptional case, where one chromatin element (possibly x) has evidently divided late and been left out in the cytoplasm; a smaller chromatin granule is also present in the cytoplasm of each spermatid.
In Sagitta this element certainly can not be regarded as a specialized spermatogonial chromosome, or as chromatin rejected from the spireme.
In the resting state it is surrounded by a membrane, and within the membrane is an intra-nuclear network made up of chromatin and linin--the chromatin is an important element.
When the chromatin is in this shape, a loop is called a chromosome.
We cannot even form a decided opinion as to whether the chromatin or the achromatin of the nuclear thread is the real idioplasm.
The process of sexual fertilization consists in the union of the male and female sex cells and an equal blending of the chromatin contained in each (Fig.
In the nucleus is a material termedchromatin which bears the factors of heredity.
The chromatin cannot itself be the hereditary substance, as it afterwards leaves the chromosomes, and the amount of it is subject to considerable variation in the nucleus, according to its stage of development.
Conjointly with the materials which take part in the formation of the nuclear spindle and other processes in the cell, the chromatin accumulates in the resting nucleus to form the nucleoli.
The chromatin is often scattered through the cytoplasm or apparently outside of it, and is sometimes difficult to see clearly.
Its nucleus is large, stains rather palely, has a delicate chromatin network, and often shows evidences of degeneration (karyorrhexis, etc.
Their chromatin is usually centrally placed, and they contain more or less coarse pigment.
Typical "segmenters" present a ring of rounded segments or spores, each with a small, dot-like chromatin mass.
The chromatinstands towards the other contents of the cell in the same relation that a nerve-element stands to any element of an organism which it excites.
The chromatin of the nucleus contains the determinants of hereditary qualities.
When, now, the egg divides, at the first and later cleavages, the chromatin masses or chromosomes contained in the double nucleus are split lengthwise and the twin portions separate to go into the nuclei of the daughter-cells.
Each of the polar bodies removes maternal chromatin from the ovum to make room for the chromatin of the fertilizing spermatozoön; but their functions are not fully understood.
Cell membrane Cytoplasm Chromatin Mitochondrion Nucleolus Endoplasmic reticulum Nucleus Nuclear membrane The basic structure of a cell is shown in Figure 2.
The main fact is that the female cells have the chromatin composition XX, the male cells the composition XY, where Y is apparently qualitatively different and often, but not necessarily, smaller than X, or entirely lacking.
Assuming it to be true that the chromatin is the important part of the cell in the matter of heredity, then it follows that we have two kinds of spermatozoa that differ from each other in a vital matter.
Driesch furnished a further proof of Boveri's law, that the final ratio of the mass of the chromatin substance in a nucleus to the mass of protoplasm is a constant in a given species.
Thus is prevented the doubling of the chromatin in the coalescence of the two nuclei at conception.
This tiny round corpuscle of chromatin now acts as a centre of attraction for the invading spermatozoon in the large ripe ovum, and coalesces with its "head," the male pro-nucleus.
Each of the polar bodies removes maternal chromatin from the ovum to make room for the chromatin of the fertilizing spermatozoön; but their functions are not fully understood.
The most characteristic feature of the nucleus is the deeply-staining, more or less vacuolated spherical karyosome (consisting of chromatin intimately bound up with a plastinoid basis) which is invariably present.
All the chromatin of the nucleus is not, however, confined to the karyosome, some being in the form of grains in the nuclear sap; and in some cases at any rate (e.
The process by which the chromatinis subdivided is so curious as to be worth a brief description.
The part of the cell which contains chromatin is called the nucleus.
In every cell division the first step consists in a division of the chromatin of the nucleus, which is followed by a division of the rest of the protoplasm.
Half the chromatinmaterial passes into each of the two cells formed.
Thus sex is inherited, like other characters, by the action of the chromatin material of the cell nucleus.
A cross section of the sperm head at such a stage as figure 87 shows the chromatin in crescent shape with material which stains very little within (fig.
Spermatids containing both the chromatin nucleolus (n) and the odd chromosome (x), a the acrosome.
In several of the species of Coleoptera and in Aphrophora, it has been shown that a body staining like chromatin develops in the spermatids, increasing in size for a time, then breaking up into granules and disappearing.
Figure 79 is a very young spermatid showing only diffuse chromatin in the nucleus.
A pair of smaller chromatin masses may sometimes be detected at this stage, and are readily found a little later (fig.
While in Tenebrio the chromatinstains very dark throughout the growth stage, and the unequal pair can not be distinguished until the prophase of division ('05, plate VI, figs.
Next to the secondary spermatogonia are cysts of young spermatocytes, whose nuclei show a continuous spireme and an elongated deeply staining chromatin rod which is the odd chromosome (fig.
A series of stages in the development of the sperm head, showing the various phases in the history of the chromatin nucleolus (n).
The smaller chromatin body seems to correspond to that described for the spermatids of Odontota dorsalis.
This is probably homologous with the chromatinnucleolus described for the spermatids of the Coleoptera.
Note that while only a small proportion of the cytoplasm passes into this tiny cell, its chromatin content is as great as that of the ovum.
If we examine this thread closely, in some forms it may be seen to consist of a series of deeply-stained chromatin granules packed closely together intermingled with the substance of the original nuclear network.
The walls of the remaining seven somatic cells have not yet formed though the resting or the dividing (M p) nuclei may be seen; c R, chromatin fragments cast off from the somatic cells.
Many biologists accept this along with other evidence as indicating that in chromatin we have a substance which is not the same throughout, that different regions of the same chromosome have different physiological values.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "chromatin" in a variety of sentences. We hope that you will now be able to make sentences using this word.
