Leukaemia cytogenetics / H. Jackson Woodliff.

  • Woodliff, H. Jackson.
Date:
1971
Catalogue details

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

Credit: Leukaemia cytogenetics / H. Jackson Woodliff. Source: Wellcome Collection.

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    CHROMOSOMAL ABNORMALITIES 29 subjects. Chromatid breaks are more complete separations of the chromatid leaving an achromatic area greater than the width of the chromatid and isochromatid breaks are similar but involve both chromatids. They may be found in a few cells from normal subjects. A chromatid fragment is a portion of chromatid com¬ pletely separated from the chromosome and chromosome acentric fragments result if there is complete separation of both daughter chromatids from the rest of the chromosomes ; this rarely occurs in normal cells. Chromatid exchanges are abnormal arrangements of two or more chromosomes formed by the reunion of broken chromatid ends (quadriradius, triradius and chromatid rings). These chromatid aberrations occur in greater numbers of cells in patients with a variety of diseases following exposure to some drugs, chemicals and viruses. Higher concentration of agents which cause accentuation of secondary constrictions may cause gaps and breaks at the same sites on the chromosomes. Atypical chromosomes are shorter or longer than normal or have an unusual centromere position; they result from deletions, translocations or horizontal divisions. Marker chromosomes are atypical chromosomes found in sufficient metaphases to constitute an abnormal cell population or clone. A deleted chromosome has lost part of its substance and a translocated chromosome contains all or part of the chromosome material from another chromosome. Di- and tricentric chromo¬ somes have two or three centromeres and are formed by the fusion of portions of two or more chromosomes. Ring chromatids may be formed by the fusion of the chromatids of one arm to form a single ring or by the fusion of both arms to form a double ring. Chromosome rings result from the fusion of the ends of a complete chromosome. An inversion of part of the chromosome may occur without morphological change. This is called paracentric inversion and the genes lie in reverse order. If the centromere is involved it is called pericentric inversion and results in the formation of an atypical chromosome. In translocation, the segment of chromosome which is broken away may rejoin at a different site and not produce a morpho¬ logical change; if, however, a translocated portion joins another chromosome it could lead to the formation of a dicentric or acentric fragment or an atypical chromosome. An isochromosome is one which results from a transverse division of a centromere so