Behaviour of meiotic univalents during metaphase I: natural variants and computer simulations.

When univalent chromosomes are present at first meiotic division, their behaviour is highly variable. In some cases, both sister kinetochores orient towards the same pole (syntely) while in others, the two kinetochores orient to opposite poles (amphitely). The former may be accompanied by recurrent pole-to-pole oscillation, although, as the present report suggests, this is not the only variation which can be found in conjunction with syntelic orientation. This study attempts to explain this diversity of orientation phenomena. A computer model was constructed which can generate all of the common univalent behaviours. Simulation experiments suggest that chromosome length is critical in determining whether amphitelic or syntelic orientation will predominate. Syntely should be common among large univalents, but oscillations will be rare or absent if the chromosome has any capacity for microtubule attachment at its non-centromeric end. It appears that gross attributes of the chromosome may influence the orientation of univalents during the first meiotic division, with consequent effects on the probability of transmission to the next generation.