End association and segregation of the achiasmatic X and Y chromosomes of the sand rat, Psammomys obesus.

In Psammomys obesus there is no pairing between the X and Y chromosomes and no chiasma formation (Solari and Ashley, 1977). It is demonstrated that ends of the axial elements of the X and Y chromosomes come together during pachytene, and regularly form at least one end-to-end junction. This achiasmatic physical connection between the ends of the X and Y persists until anaphase I, thus assuring the normal distribution of the sex chromosomes observed by light microscopy. In addition, there are no differentiations of the axes of the X and Y similar to those observed in other mammalian species thus far examined, a fact that could influence chromatid cohesiveness and disjunction.