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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    Chapter IV CHROMOSOMAL ABNORMALITIES Introduction The preceding chapter dealt with the normal human karyotype and the variations which could occur in the normal population: this chapter is concerned with the abnormalities that might be expected in disease or following exposure to various agents either in vitro or in vivo. For convenience, they are divided into numerical and morphological variations, although both are often present in the same cell or in different cells from the same organism. Some¬ times more than one cell hne with one or more abnormal clones or a mixture of abnormal clones may be present in the same material ; this is called mosaicism. Numerical Variations Deviations from the normal haploid, diploid or polyploid number of chromosomes is called aneuploidy and occurs to a limited extent in cells from normal subjects. Five per cent aneu¬ ploidy in the peripheral blood and 10 per cent in the bone marrow can be taken as the upper limit of normal although a greater aneuploidy may be found in cells from some apparently normal subjects. Both hypodiploidy (less than 2n chromosomes) and hyperdiploidy (more than 2n chromosomes) may be produced by uneven division ; if during metaphase more chromosomes (say 47) go into one daughter cell and less (say 45) into another, the progeny of such cells, if viable, will be aneuploid. This may apply to both meiotic and mitotic divisions and is called non-disjunc¬ tion; it is a failure of the two members of a chromosome pair to separate at metaphase. A similar state of affairs occurs if chromo¬ somes do not line up properly during the spindle phase or fail to move at anaphase with the result that they may be included in the wrong daughter cell or not included in either. Increased aneuploidy is found in a variety of diseases or following various treatments; it may be due to random drop out or increase of