C-heterochromatin and chiasma terminalization in the jerboas Allactaga and Jaculus (Rodentia : Dipodidae)

C-heterochromatin and chiasma distribution patterns of meiotic chromosomes were studied in the dipodids Allactaga tetradactyla, Jaculus jaculus jaculus and Jaculus orientalis and chiasma terminalization was discussed. Darkly stained C-band located at the centromeric region of some bivalents was observed in all species at diakinesis and metaphase I. Of the occurrence of C-heterochromatin in the 24 bivalents, J. orientalis exhibited the highest percentage of absence of the C-blocks, where it was 68.8\%, compared to 18.8\% in A. tetradactyla and 14.6\% in J.j.jaculus. Analysis of variance of the means of relative distances of interstitial and terminal chiasmata from the centromere in the larger bivalents no. 1 and 2 of each species at diakinesis and metaphase I showed that the interstitial chiasmata are stable in their positions at the two stages and do not move to the chromosome termini, while the terminal chiasmata scored at diakinesis are in fact achiasmatic terminal associations and some of them gradually terminalize at metaphase I. Therefore, it is concluded that C-heterochromatin pattern of meiotic chromosomes is quite similar to that of mitotic chromosomes except the pair no. I in A. tetradactyla, stability of interstitial chiasmata at the two stages might negate the idea of chiasma terminalization and C-heterochromatin has not any role in the distribution of chiasmata.