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Updated: May 10, 2025
All of these cells will, of course, contain four chromosomes; and, what is more important, half of the chromosomes will have been derived directly from the male and half from the female parent. Even into adult life, therefore, the cells of the animal probably contain chromatin derived by direct descent from each of its parents.
The factor for red eye occurs in the sex-chromosomes, that is to say, according to this theory, the sex-chromosome does not merely determine sex but carries other factors as well, and this fact is the explanation of sex-linked inheritance. The factor for red eye then is present in both X chromosomes of the wild female, absent from both X and Y chromosomes of the white-eyed male.
In two of these pairs the chromosomes are elongated and shaped like boomerangs, in the third they are small, round granules, and the fourth pair are the sex-chromosomes: in the female these last are straight rods, in the male one is straight as in the female, the other is bent. The straight ones are called the X chromosomes, the bent one the Y chromosome.
==The Significance of Fertilization.== From this process of fertilization a number of conclusions, highly important for our purpose, can be drawn. In the first place, it is evident that the chromosomes form the part of the cell which contain the hereditary traits handed down from parent to child.
It is evident that what Dr. Wilson means is that the sex-chromosome is unpaired, and that although it divides like the others in the homotypic division, in the heterotypic division it has no mate and so passes with half the number of chromosomes to one pole of the division spindle, while the other group of chromosomes has no sex-chromosome.
If we accept the idea that characters are represented by particular parts of the chromosomes, according to Morgan's scheme, our theory of development is the modern form of the theory of preformation.
This gives the physical basis for paternal inheritance as well as for maternal inheritance, and it shows why they may be of the same or equivalent degree. 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.
In occasional individuals the factors whatever they are, portions of the chromosomes or arrangement of the chromosomes or anything else, are different from those of the normal egg, and in consequence the abnormalities above described are developed.
The fine-spun, elaborate theories about sex, so current twenty years ago, have fallen into almost complete desuetude among scientists. With the discovery of the place of the chromosomes in inheritance, biologists began to give their almost undivided attention to a rigid laboratory examination of the cell.
But lost in her own bitterness, she could give him no sign. So he sighed, and said simply. 'Kataya and I had hoped that perhaps Ishmael..... But he's gone now, and who knows if we'll ever see him again, or even if his chromosomes would match. 'Ishmael will come back, answered Kalus seriously, the doctor's words largely lost on him, but wanting to ease Kataya's pain.
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