The X-chromosome of the chinchilla is the largest member of the complement. Since its area equals approximately 9% of that of the haploid autosome set, it may represent a “duplicate-type X-chromosome”, in contrast to the “original-type” in which the ratio X:autosomes ranges from 5 to 6.5%. Unlike other known species with the “duplicate-type X-chromosome”, the chinchilla possesses a very small Y-chromosome.
It was inferred from the allocyclic behavior and asynchronous replication pattern of the sex chromosomes in somatic cells that one X-chromosome in the female and the male X-chromosome manifest a single genetically active region: the presumed active segment is inserted in the longer arm adjacent to the centromere. The remainder of these X-chromosomes, the entire second X-chromosome in the female and the Y-chromosome displayed positive heteropycnosis in mitotic prophase and completed DNA synthesis prior to mitosis later than any other elements: this cytologic behavior was held to reflect genetic inertness.
The existence of genetic inactivation of much of the “duplicate-type” X-chromosome mass of the chinchilla supports the hypothesis that a constant optimal ratio between the functional portion of the X-chromosomes and the autosomes is maintained in mammals despite a wide range of relative sizes of the X-chromosomes.
In female meiosis there is a free exchange of chiasmata between the X-chromosomes at first meiotic metaphase. In the male, however, the association between the large X- and small Y-chromosomes during meiosis is invariably end-to-end, denoting the absence of synapsis. This contrasts with the occurrence of side-by-side pairing of the XY-bivalent in other mammals possessing the “duplicate-type X-chromosome” but in which the Y-chromosome is correspondingly large.
Interphase Nucleus Late Replication Meiotic Metaphase Female Meiosis Genetic Inactivation
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Barr, M. L.: The sex chromatin. In: Intersexuality (ed. C. Overzier), p. 48–71. New York: Academic Press 1961–1963.Google Scholar
Bennett, E. T.: On the Chinchillidae, a family of herbivorous Rodentia, and on a new genus referrible to it. Trans. zool. Soc. Lond. 1, 35–64 (communicated 1833; published 1835).CrossRefGoogle Scholar
Beutler, E., M. Yeh, and V. F. Fairbanks: The normal human female as a mosaic of X-chromosome activity: studies using the gene for G-6-PD-deficiency as a marker. Proc. nat. Acad. Sci. (Wash.) 48, 9–16 (1962).CrossRefGoogle Scholar
Fredga, K., and B. Santesson: Male meiosis in the Syrian, Chinese, and European hamsters. Hereditas (Lund) 52, 36–48 (1964).Google Scholar
Galton, M., and S. F. Holt: DNA replication patterns of the sex chromosomes in somatic cells of the Syrian hamster. Cytogenetics 3, 97–111 (1964); - Asynchronous replication of the mouse sex chromosomes. Exp. Cell Res. 37, 111–116 (1965).CrossRefPubMedGoogle Scholar
Hopkins, T. F., and L. M. Whidden: The demonstration of a sexual dimorphism in liver cells of the rodent Chinchilla laniger. Exp. Cell Res. 18, 178–179 (1959).CrossRefPubMedGoogle Scholar
Hsu, T. C., W. Schmid and E. Stubblefield: DNA replication sequence in higher animals. In: Role of chromosomes in development (23rd Symp. Soc. Study Developm. Growth, ed. M. Locke), p. 83–112. New York: Academic Press 1964.CrossRefGoogle Scholar
Huang, C. C., and L. C. Strong: Chromosomes of the African mouse. J. Hered. 53, 95–99 (1962).PubMedGoogle Scholar
Lyon, M. F.: Gene action in the X-chromosome of the mouse (Mus musculus L.). Nature (Lond.) 190, 372–373 (1961).CrossRefGoogle Scholar
Makino, S.: Notes on the chromosomes of the porcupine and the chinchilla. Experientia (Basel) 9, 213–214 (1953a); - Chromosome numbers of some American rodents. Science 118, 630 (1953b).CrossRefGoogle Scholar
Matthey, R.: Cytologie comparée des Cricetinae paléarctiques et américains. Rev. suisse Zool. 68, 41–61 (1961).Google Scholar
Moorhead, P. S., P. C. Nowell, W. J. Mellman, D. M. Battips, and D. A. Hungerford: Chromosome preparations of leukocytes cultured from human peripheral blood. Exp. Cell Res. 20, 613–616 (1960).CrossRefPubMedGoogle Scholar
Nes, N.: The chromosomes of Chinchilla lanigera. Acta vet. scand. 4, 128–135 (1963).Google Scholar
Ohno, S., W. Beçak, and M. L. Beçak: X-autosome ratio and the behavior pattern of individual X-chromosomes in placental mammals. Chromosoma (Berl.) 15, 14–30 (1964).CrossRefGoogle Scholar
, and T. S. Hauschka: Allocycly o the X-chromosomes in tumors and normal tissues. Cancer Res. 20, 541–545 (1960).PubMedGoogle Scholar
Ohno, S., and C. Weiler: Relationship between large Y-chromosome and side-by-side pairing of the XY-bivalent observed in the Chinese hamster, Cricetus griseus. Chromosoma (Berl.) 13, 106–110 (1962).CrossRefGoogle Scholar