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Updated: July 10, 2025
The Mendelian theory therefore is that when an ovum has two X sex-chromosomes it can only after a number of cell-divisions, at the following reduction division, give rise to ova, while an ovum containing one X sex-chromosome, or two different, XY, chromosomes, at the next reduction division gives rise to spermatozoa.
Whether the mixture of the chromosomes occurs in every resting stage of the nucleus in the successive generations of the gametocytes, or whether it occurs only in the synapsis stage preceding reduction division, it is not surprising that the colloid substance of the chromosomes should form a more or less complete intermixture, and that the two original chromosomes should not be again separated in the pure condition in which they came into contact.
Haploids don't reproduce, and the only way the diploid number of chromosomes can be kept is to replace those lost by maturation division of the ovum. You might be able to keep the diploid number by using immature ova, but the fertilization technique would be far more complex than the simple uterine injections you use at Hillside Station." Douglas looked at him blankly.
Moreover, the various fibres which surround the centrosomes in cell division and whose contractions and expansions, as we have seen, pull the chromosomes apart in cell division, are parts of the cell substance. All of these are the results of destructive metabolism, and we must, therefore, conclude that destructive processes are seated in the cell substance.
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.
This follows from the fact that the chromosomes are the only part of the cell which, in the fertilized egg, is derived from both parents. Now the offspring can certainly inherit from each parent, and hence the hereditary traits must be associated with some part of the cell which is derived from both.
But the egg substance is derived from the mother alone; the centrosome, at least in some cases and perhaps in all, is derived only from the father, while the chromosomes are derived from both parents. Hence it follows that the hereditary traits must be particularly associated with the chromosomes. With this understanding we can, at least, in part understand the purpose of fertilization.
"It's merely a routine inspection," murmured Nuwell. Goat indicated one of his charts, showing a diagram of genes and chromosomes in different colors. "This is my original chart," he said. "I copied it from one belonging to the Martians many years ago, and my genetic alteration of Brute and Adam were based on it.
The theory proposed by me in 1908 was that we have within the gonads numerous gametocytes whose chromosomes contain factors corresponding to the different parts of the soma, and that factors or determinants might be stimulated by products circulating in the blood and derived from the parts of the soma corresponding to them.
In all the changes which follow these asters lead the way. When they reach this position they are still surrounded by the radiating fibres, and connected by the spindle fibres. During this time the chromosomes have been changing their position.
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