Specific chromosome anomaly associated with autonomous and cancerous development in man

Cytogenetic studies of Haplopappus gracilis in both callus and suspension cell cultures

Investigations have been carried out on karyotype change in both callus and suspension cell cultures of Haplopappus gracilis (2n=4). It has been found that polyploidization arises directly in culture to give up to six times the normal diploid chromosome number in some cultures. In polyploid cultures, both chromosome loss and chromosome rearrangements occur to give rise to aneuploid karyotypes displaying chromosomes which differ in morphology from the diploid set. Whole or partial chromosome loss has been observed in the form of lagging chromosomes and chromosome bridges at anaphase, and micronuclei, ring chromosomes and chromosome fragments at other stages in mitosis. C-banded preparations have confirmed the occurrence of chromosomal rearrangements. Comparative investigations suggest that (i) more polyploidy occurs in callus cultures than in suspension cell cultures, and (ii) the presence of cytokinin (kinetin) in the culture medium may reduce the extent of karyotype change.

Non-random chromosome changes in human cancer

Chromosome changes in human cancer cells appear to evolve by non-random losses and/or gains of particular homologues or groups. It is probable that some of the apparent losses or gains actually represent formation of new chromosome structures, which are then classified as markers or are misclassified as normal homologues. In many cancers these changes appear to continue at a high rate throughout the life of the cancer (so that in some cancers almost every cell will exhibit a different karyotype). In other cancers the rate of change may be slow or arrested so that all cells will have the same abnormal karyotype. One very common step in karyotype evolution is doubling of the entire chromosome complement (2n → 4n or more commonly, S → 2S where S is the stemline number). The 2S cells tend to replace the original stemline. Homologues which have larger amounts of concentrated blocks of heterochromatin (i.e. late replicating DNA) seem more apt to be lost.

Chromosome 16: a specific chromosomal pathway for the origin of human malignancy?

Minkler, Gofman and Tandy (1970a, b) have recently reported data on the karyotype constitutions of human tissue culture cell lines and human tumours, as gathered by a semi-automatic chromosome analysis system. The data appears to show a relationship between the relative number of "number 16" chromosomes and malignancy. We have tested the ability of the "cutting line" approach they used to correctly classify chromosomes from a sample of 723 cells from 100 normal subjects. The cutting line scheme gave very different results from those of an experienced cytogeneticist. The method also failed to give correct average numbers of chromosomes per class. We are thus led to question the conclusions reached by Minkler et al. It appears possible that their relatively consistent finding of an excess of "number 16" chromosomes in their largely hyperploid material may be an artefact of their classification scheme, arising from measurement normalization problems, rather than a reflection of a real excess of "number 16" or even of "number 16-like" chromosomes.