The location of notch in the X chromosome was not determined by Dexter, but the mutant has appeared anew three or four times and the position has been found by Bridges to be approximately at 2.
In the latter case an egg without an X chromosomeis produced.
Therefore, if an abnormal male is mated to a wild female the daughters are heterozygous for abnormal, while the sons, getting their X chromosome from their mother, are entirely normal.
Triple crossing-over in the X chromosomeis extremely rare and has been observed only about a half dozen times.
Farther evidence against this supposition is that females that have one X chromosome with both yellow and white and the other X chromosome with yellow, lethal, and white are exactly like regular stock yellow white flies.
A preliminary test was made by mating with eosin, whose factor lies near the left end of the X chromosome series.
Both the X and the Y sperm have been shown to produce the sex opposite to that which they normally produce when they fertilize eggs that are normal in every respect, except that of their X chromosome content.
It is evident from these data that there must be present in the sex-chromosome a gen that causes the death of every male that receives this chromosome, and that this lethal factor lies very close to the factor for white eyes.
The lethal must have appeared in a chromosome which was already carrying white and yet did not affect the character of the white.
Every sexual differentiation in organisms, which occurred in the course of phylogenetic development, was followed by fertilisation and therefore by the creation of a diploid or double-chromosome product.
Each half-chromosome is connected with one of the spindle poles only and is then drawn towards that pole.
The accessory chromosome has been now observed in most of the great divisions of insects (As Wilson has proved, the unpaired body is not a universal feature even in those orders in which it has been observed.
When the separation of these chromosomes and their distribution to both daughter-nuclei occur a chromosome of each kind is provided for each of these nuclei.
Boveri found that in the case of the doubly fertilized egg the isolated "1/4" blastomeres develop very variously, a variability only to be accounted for by their varying chromosome equipment.
Weismann believes the determinants to be grouped into complex bodies called ‘ids,’ each id containing all the determinants necessary for a whole being, and each chromosome being composed of a number of ids.
This partition has to be qualitative as well as quantitative; for one chromosome may, and no doubt does, differ in function and influence from another, and has various elements within itself.
A chromosome is not, or is not usually, a simple body.
Both the secretory action and the chromosomemechanisms are different.
Of the 24 chromosomes in each sperm or egg we are here concerned with only one, known as the sex chromosome because, in addition to transmitting other characteristics, it determines the sex of the new individual.
If a sperm and egg both carrying the X-type of chromosome unite in fertilization, the resulting embryo is a female.
The chromosome mechanisms practically force us to suppose that about half the eggs are originally predisposed to maleness, half to femaleness.
The result is that the gametes (sperm and eggs) they respectively produce in maturation are not exactly alike as to chromosome composition.
At anaphase the sister chromatids of each chromosome separate, and each part moves toward the ends, or poles, of the cell.
In A and B, the midportion of DNA synthesis, the radioisotope is distributed throughout the chromosome arms; in C, near the end of DNA synthesis, it is confined mainly to the end of the arms.
The chromosome corresponding to the larger member of the unequal pair in the male evidently has a homologue of equal size in the female.
The odd chromosome of the Elaters stains less deeply than the others in the first spermatocyte.
It also assumes that the large female sex chromosome is dominant in the presence of the male sex chromosome, and that the male sex chromosome is dominant in the presence of the small female sex chromosome.
Here the odd chromosome is more condensed, or shortened, and split.
All of the second spermatocyte metaphases in which a small chromosome occurred, contained two small ones, making 9 in all (fig.
On the morphology of the chromosome group in Brachystola magna.
In figure 94, a spermatogonial metaphase, the smallchromosome is shown with 17 larger ones.
Here the components of the unequal pair are the small spherical chromosome and one of the several chromosomes third in size, forming a comparatively small unsymmetrical bivalent (figs.
Resting nucleus of a young oocyte before synapsis, showing two pairs of condensed chromosomes, corresponding in size to the m-chromosomes and the odd chromosome of the spermatocytes.
The oddchromosome is always more or less eccentric and is attached by a spindle fiber to one pole.
Beginning of division of protoplasm; the two parts of each chromosome separated.
This crossing over of determiners from one chromosome to another takes place only among such as are actually in contact at times within the nucleus as seen under the microscope, which confines it to the members of corresponding pairs.
This grouping of the determiners, several to a chromosome, carries an interesting consequence with it, in that all the hereditary traits controlled by one chromosome have to go together in reproduction.
The chromosomes now become arranged at the middle of the spindle, and apparently each chromosome becomes fastened to a thread.
This means that the cells of the germinal tissue of females have 24 complete pairs, while the corresponding cells in males have only 23 complete pairs and one chromosome over.
Suppose we have two parents, both of whom are hybrids in respect to chromosome pair one.
The single-sex chromosome which males possess invariably comes from the mother.
The evidence indicates that this is not a virus trouble, but a systemic defect, probably caused by chromosome aberration or gene abnormality.
Exactly the opposite situation is found in the related family of alders and willows where the chromosome number is very variable.
This indicates that there may be a difference inchromosome count.
The whole question of chromosome number in nut varieties and species is as follows.
A number of years ago I examined the chromosomes of one of these large fruited varieties, and it had the same chromosome number as the others, namely sixteen pairs or thirty two.
The pines, and all other cone-bearing trees make up another very large group in which chromosome numbers are constant.
All of the species of Castanea, as far as we know, have the same chromosome number, and all of the varieties within each species have the same number.
Second, doubling of the chromosome number makes possible hybridization of individuals heretofore unsuccessful in such effort.
This fact agrees with the hypothesis that the factors in such a case are contained in a single chromosome which segregates from the fellow of its pair in the reduction divisions.
Various attempts have been made to explain gynandromorphism in insects in accordance with the chromosome theory of sex-determination.
He remarks that the X chromosome must be a male-determining factor since in many cases it is the only sex-chromosome in the males, yet its introduction into the egg establishes the female condition.
On the other hand, we have the evident fact that a number of chromosomes formed apparently of the same substance, by a series of equal chromosome divisions determine all the various special parts of the complicated body.
The ovum then with one X chromosome or one X and one Y changes its sex at the next reduction division and becomes male.
The fertilised female ova therefore carry an X red chromosome + an X white chromosome, the male producing ova one X red chromosome and one Y white chromosome.
The sex is thus determined by the male gamete, the X chromosome united with that of the female gamete producing female individuals, while the Y united with X produces male individuals.
Now when lata is produced it is believed that in the heterotypic division one pair passes into one daughter-cell instead of one chromosome of the pair into each daughter-cell, the other pairs segregating in the usual way.
You've a chromosome and I haven't, and look at us.
That, Amory thought, was the funny aspect; the nauseating one came when you remembered that, properly diffused by this same means, really valuable information about Eugenics and the Chromosome might have been given to the world.
I did my best for her; I tried to explain what a chromosome was; but it was no good.
Flemming had seen in the Salamander twenty-four chromosome fibers, which seems to be a constant number in the cells of epithelium and connective tissues.
On the dynamical theory, the chemical and physical energy in the centrosome might influence the cell plasm and the nucleus and attract the chromosome elements of the nucleus to the poles of the spindle.
As the threads stain when coloring agents are applied to them, they are called chromatin fibers, and the loose coil is the chromosome (Waldeyer).
An equatorial plate is formed and each chromosome has split into two halves by longitudinal division.
Each half of each chromosome separates from its fellow, and moves to the opposite end of the nucleus toward the two centrosomes (Fig.
It consists in the splitting of eachchromosome into two equal halves.
Each chromosome splits lengthwise into exactly similar halves, and these, in the Anaphases of the mitosis, drift out to the opposite poles of the spindle to form the daughter-nuclei of the new cells.
Id is a word derived from Naegeli's term idioplasm, which means the chromosome granule.
Chromosome counts from as few as 23 meiotic cells of S.
Diploid (2n) chromosome numbers were determined from cells in late prophase and metaphase of mitosis.
Haploid (n) chromosome numbers were determined from cells in diakinesis, metaphase I, and metaphase II of meiosis.
Each chromosomesplits lengthwise to form two daughter chromosomes which then diverge to pass to the poles of the spindle (Figs.
It is true that there are more pairs of characters than pairs of chromosomes but there is no reason for supposing that a given chromosome is restricted to carrying a single unit-determiner.
The normal sex-chromosome is indicated by a black =X=, the one lacking the factor for color perception, by a light X.
In the males of such animals this chromosome is present in addition to the regular number of pairs, thus giving rise to an uneven instead of the conventional even number of chromosomes.
The evidence centers about a special chromosome or chromosome-group commonly designated as the sex-chromosome or X-element, which has been found in various species of animals, including man.
Moreover each set is a duplicate of the other, because the substance of any individual chromosome in one group has its counterpart in the other.
A Single Chromosomenot Restricted to Carrying a Single Determiner.
Diagram illustrating the inheritance of a sex-limited character such as color-blindness in man on the assumption that the factor in question is located in the sex-chromosome (from Loeb after Wilson).
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.
A brief account of a chromatin element resembling the accessory chromosome in Sagitta has been added for comparison.
In many cases the split, if it appears at all, closes quickly and the chromosome bends in U-shape, as in figure 109, plate IV.
McClung is inclined to believe that the accessory chromosome is an element common to all of the male reproductive cells of Arthropods, and probably to vertebrate spermatocytes as well ('02).
Stage similar to 18a, one chromosome in double diamond form.
In these latter stages the nucleolus has entirely faded out and nothing suggesting an accessory chromosome is present.
The eggs have so far resisted all efforts to learn what part the odd chromosome may play in fertilization.
In figure 130 one lagging chromosome shows the dyad nature of the products of the division of the tetrad.
The safranin-gentian combination used by Miss Wallace and others in the study of the accessory chromosome did not prove to be especially helpful with these forms.
Montgomery regards them as "chromosomes that are in the process of disappearance in the evolution of a higher to a lower chromosome number.
The two possible chromosome combinations between egg and spermatozoa are therefore as follows (see the diagrammatic Fig.
According to the chromosome theory of Mendelian heredity a differs from A in one point, though this difference is probably only of a chemical character and not visible.
The homologous chromosome in beans with white colour may be designated as a.
Wilson made sure that all the eggs are alike in the number of chromosomes, each egg containing an X chromosome in addition to the six chromosomes characteristic of the species Protenor.
Wilson showed that in those cases where there are two types of spermatozoa, one with and one without an accessory or as it is now called an X chromosome, all the cells of the female have one chromosome more than the cells of the male.
If an egg with A is fertilized by a pollen with a (or vice versa), after fertilization thechromosome constitution of the fertilized egg is Aa.
This is intelligible on the assumption that the unfertilized egg contains only one X chromosome while the spermatozoon carries into the egg the second X chromosome.
In the process, when the chromosome number is halved among the females, 11 go into each mature egg.
It has been found that the twenty-two chromosome individual invariably develops into a female, and the twenty-one into a male.
The current explanation is that such traits happen to be in the same chromosome as the determiner of maleness or femaleness, as the case may be.
In the above illustration four different views of the nucleus of the germ-cell of an earthworm are shown, with the chromosomes in different stages; in section 19 each chromosome is doubled up like a hairpin.
The chromosomecycle of gregarines, with special reference to Diplocystis schneideri Kunstler.
Studies on Gregarina blattarum with particular reference to the chromosome cycle.
Every notch winged female has one X chromosome that carries the factor for notch and one X chromosome that is "normal".
Any egg fertilized by a Y-bearing sperm will become a male with white eyes because the only X chromosome that the male contains comes from his mother and is white producing.
At the other division each chromosome simply splits as in ordinary cell division.
Other evidence has shown that the Y chromosome of the male is indifferent, so far as these Mendelian factors are concerned.
Any egg fertilized by a Y-bearing sperm will produce a male that will also have red eyes because he gets his (black) X chromosome from his mother.
The normal chromosome group of the female is shown in figure 52 and the chromosome group of one of the exceptional females is shown in figure 69.
Drosophila the chromosome explanation is the same.
The X chromosome in the male is represented by an open bar, the Y chromosome is bent.
A black rod indicates that the chromosome carries the factor for red; the open chromosome the factor for white eye color.
Any egg fertilized by an X bearing sperm will produce a female that will have red eyes because the X (black) chromosome it gets from the mother carries the dominant factor for red.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "chromosome" in a variety of sentences. We hope that you will now be able to make sentences using this word.
