Genetics in obstetrics and gynecology / Joe Leigh Simpson [and others].

Date:
[1982], ©1982
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Genetics in obstetrics and gynecology / Joe Leigh Simpson [and others]. Source: Wellcome Collection.

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    PRINCIPLES OF HUMAN GENETICS / 7 Short arm (p) Centromere Long arm (q) Such bands are defined either by regions of fluorescent intensity differences (Q-bands) or by regions that stain lighter or darker than adjacent regions (G-, R-, or C-bands). Additional cytogenetic information concerning sex chromosome consti¬ tution can be obtained by analysis of interphase nuclei derived from buccal epithelial cells and other tissues; however, these studies almost never suffice without additional genetic studies. X chromosomes in excess of one become inactivated and form X-chromatin masses (formerly known as sex chromatin or Barr bodies] (Fig. 1-5). The manner by which inactivation is accomplished is unknown, but it involves coiling because inactive X chromosomes are the last of the complement to replicate their DNA (late-replicating X). The number of Y chromosomes can also usually be determined from in¬ terphase cells. After addition of quinacrine and analysis with fluorescent mi¬ croscopy, the distal two thirds of the long arm of the Y chromosome fluoresces brilliantly in interphase nuclei, in metaphase, and throughout the cell cycle. The fluorescent spot produced by the Y during interphase is called Y-chromatin (Fig. 1-6), and the number of Y chromosomes equals the amount of Y-chromatin per cell. However, the testicular determinants are located not in the fluorescent but in the nonfluorescent region of the Y, near the centromere (German, Simp¬ son, & McLemore, 1973b; Simpson, 1976), so males lacking Y-chromatin may ::::: Figure 1-4. Parts of a chromosome. Figure 1-5. Interphase cell showing X-chromatin (arrow). (From Simpson JL: Disorders of Sexual Differentiation. Etiology and Clinical Delineation. New York: Academic Press, 1976, p 29. Reprinted with permission.)