ISSN:
1432-0886
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary From the 15 diverse species of placental mammals investigated cytologically in this laboratory, seven species and one interspecific hybrid were selected for the present study : man (Homo sapiens, 2n=46), cattle (Bos taurus, 2n=60), the cat (Felis domestica, 2n=38), the dog (Canis familiaris, 2n=78), the mouse (Mus musculus, 2n=40), the golden hamster (Mesocricetus auratus, 2n=44), the creeping vole (Microtus oregoni, 2n=17/18), and the mule (2n=63). We devised a method for making two-dimensional measurements of chromosomes which produced the following results: 1. Despite the wide variation in chromosome number, the eight species had diploid chromosome complements which appeared to contain about the same amount of genetic material, varying from 145.14 μ2 in the mouse to 165.73 μ2 in cattle. 2. The X-chromosome of the dog, the donkey, and cattle appeared to be almost identical in absolute size, ranging from 4.11 to 4.65 μ2. Although only presumptive identification of the X is possible in the cat, the mouse, man, and the horse, they too seemed to fall within the same size range (3.75–5.07 μ2). Phylogenic studies of vertebrate sex chromosomes suggest that the X in the great majority of placental mammals retains the original size and genetic constitution of a common ancestor. In the golden hamster, the X is twice this size (8.33 μ2) and is regarded as a duplicate; in the creeping vole, three times (12.70 μ2), a triplicate. In the latter species, the sex chromosome constitution of somatic cells in the normal female is XO. 3. Each of the three X-chromosome types demonstrated a distinctive behavior pattern in somatic cells. If positive heteropycnosis can be equated with genetic inertness, then all the species in this study appeared to have about the same amount of functioning X-chromosome material in diploid nuclei of both sexes. The ambivalent nature of the mammalian X apparently provides the mechanism which maintains the constant optimal ratio between the functional X and the autosomes in somatic cells.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00326912
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