Contribution of reciprocal translocations to an understanding of chromosome displacement: inferences for studies of spatial order at metaphase.

Chromosome displacement was analysed in three different translocations. Two alternative hypotheses were examined: (1) Displacement is determined by the spatial ordering of chromosomes on the metaphase plate. (2) Displacement is a function of the gross physical property of chromosome size and does not reflect ordering. Predicted numbers of displacements were calculated for each chromosome for each of the two hypotheses and these were compared with the observed numbers of displacements using a chi 2 analysis. In the analysis for two of the three translocations, the first hypothesis was rejected whilst the alternative hypothesis was supported by all three analyses. It is concluded that chromosome displacement is a function of chromosome size and does not reflect spatial ordering at metaphase. Furthermore, it is suggested that many studies of apparent ordering at metaphase may merely reflect chromosome displacement. The analysis of displacement rates in all other chromosomes of the complement was undertaken in one of the translocation carriers. This showed no alteration of relative displacement rates.