Chromosome Analysis of Abnormal Cells

Abstract

THE karyotype of a somatic cell is the pattern obtained by the arrangement of the chromosomes into various groups by length and centromere position. The average forms of all chromosomes of a complement are defined by an idiogram, based on a large number of karyotypes. The human diploid idiogram was standardized at the Denver¹ and London² conferences on human chromosomes. By comparing normal or near normal karyotypes with the standard, it is possible without any supporting genetic data to identify changes in chromosome structure. When the cells have been taken directly from the diploid organism or when they have been in culture for only a short time, it is legitimate to ignore the numerous small shape differences, such as variations in coiling or artefacts, from the Denver–London idiogram. But when a cell population is known to be distantly descended from the parent diploid—for example, when it has been long in culture—and if the chromosome complement has changed both numerically and structurally, then comparison with the diploid idiogram is more difficult. Changes in chromosome structure are likely to have been numerous, and shape alone is not a valid criterion for chromosome identification.