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.

    22/344 (page 8)
    10 / GENETICS IN OBSTETRICS AND GYNECOLOGY DNA of most eukaryotes, contains aggregates of repeated nucleotide sequences that are not complex enough to code for proteins. This repetitious DNA may protect DNA that codes for proteins or may synthesize simple structural com¬ ponents like rRNA or histones. The mechanism of chromosome banding has been reviewed by several authors (Comings et al., 1973; О. J. Miller et al., 1973a, 1973b; Dutrillaux & Lejeune, 1975]. Positive C-bands probably represent one of several kinds of repetitive DNA, but no single explanation is universally accepted for Q-, G-, and R-bands. Banding may be related to variations in DNA base sequences along chromosomes; in particular, positive Q- and G-band regions appear to be rich in adenine-thymine (AT) pairs (O. J. Miller et al., 1973a). How^ever, base sequence changes cannot entirely explain banding patterns (Comings, 1974). Thus, Q-, G-, and R-bands may reflect variations not only in base com¬ position but also in the nature or quantity of proteins bound to DNA; that is, bands may reflect DNA-protein interaction. CYTOGENETIC NOMENCLATURE An official chromosomal nomenclature exists, adherence to w^hich not only permits the chromosomal complement to be designated in a standard manner requiring no additional explanation, but also increases accuracy of commu¬ nication. Table 1-2 lists some symbols used to designate parts of chromosomes and certain rearrangements. Chromosomes are identified by distinctive landmarks. The areas betwreen adjacent landmarks are called regions. Chromosome bands are numbered according to a particular system, an example of which is shown in Figure 1-7. A band is designated by listing the chromosome, the arm (p or Table 1-2 Some Symbols Recommended by the Paris Conference (1971) and Supplement (1975) From Simpson JL, Martin AO: Cytogenetic nomenclature. Am J Obstet Gynecol 128:167, 1977. Reprinted with per¬ mission.