Cytogenetics of the parthenogenetic grasshopper Warramaba (formerly Moraba) virgo and its bisexual relatives. VI. DNA replication patterns of the chromosomes.

The distribution of late-replicating segments along the chromosomes of five clones of W. virgo is described. Some, but not all of these segments correspond to C-bands. In general, the "autoradiographic profiles" (histograms of linear grain density along the length of chromosomes labeled with tritiated thymidine in late S-phase) show strong resemblances throughout the five clones. However, some significant differences exist, and these are particularly marked in the case of the Boulder clone, which is anomalous in many other respects. --A similar study has also been carried out on the two bisexual species of Warramaba ("P169" and "P196") that gave rise, by hybridization more than half a million years ago, to the parthenogenetic W. virgo. In the case of P169, the autoradiographic profiles of the three large chromosomes (X + A, B + 5, CD) which it has contributed to the W. virgo karyotype are extremely similar to those of the corresponding chromosomes in the virgo clones we have studied. In the case of P196 there is likewise, in most instances, a close resemblance of the autoradiographic profiles of the AB, X1 and CD chromosomes to those of the same chromosomes in the virgo clones, but that of the X1 shows no particular resemblance to the anomalous profile of the X1 in the Boulder clone, in which the X1 has undergone a structural reorganisation. The autoradiographic profile of the P196 CD chromosome does, however, show a much closer resemblance to that of the corresponding chromosome in the Boulder clone than to those of the CD196 in the other four virgo clones studied. These investigations confirm the considerable evolutionary stability of DNA replication patterns.