Abstract
WHEN a cell divides to produce two daughter cells having the same genetical properties as itself, the nucleus resolves itself into a definite number of structures, the chromosomes. These, splitting lengthwise, give rise to two identical groups which go to make the daughter nuclei. In this process, known as mitosis, it is evident that, with certain exceptions which need not be gone into here, the chromosomes into which the nucleus resolves itself are always identical in number and form with those which went to constitute it at the preceding division. The chromosome number is said to be constant. It follows that when, in the course of sexual reproduction, two germ-cells unite to form a zygote and their nuclei fuse, the new generation of cells thus established will show at mitosis a new chromosome outfit or ‘complement’, the sum of those of the two germ-cells. When these are identical the number will be simply doubled, and in these circumstances the number of chromosomes in the germ-cell is said to be ‘haploid’ and the double number of the zygote is said to be ‘diploid’ (see Fig. 1). Further, when the FIG. 1.—The diploid chromosome number (24) in a root tip of Tulipa Clusiana, a form from Tibet. new zygote comes to produce germ cells, which by their union will reconstitute a diploid individual like itself, the zygote nuclei undergo a process of ‘reduction’, by which a new cell generation is produced having the haploid number of the gametes.
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DARLINGTON, C. Polyploids and Polyploidy. Nature 124, 62–64 (1929). https://doi.org/10.1038/124062a0
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DOI: https://doi.org/10.1038/124062a0