A highly repeated DNA from the genome of the wallaroo (Macropus robustus robustus)

The major satellite of M. r. robustus DNA has been isolated in a Ag+-Cs2SO4 gradient. It has a density of 1.710 g/cm(3) compared with 1.697 g/cm(3) for the bulk of the DNA, and accounts for about 10% of the total DNA. Sequence heterogeneity within the satellite was shown by an increase in density to 1.715 g/cm(3) and by a reduction of 12 degrees C in the temperature of denaturation (Tm) after renaturation. The satellite was found to occur in the centromeric regions of all chromosomes. This pattern of distribution was essentially duplicated in the genomes of other members of the wallaroo group. A polymorphism for a major block of the sequences on chromosome 5 occurred in both M. r. erubescens and M. antilopinus. Species in the wallaroo group all contained about the same amount of this sequence, while M. rufus contained 30% and M. rufogriseus 16% of the wallaroo content; all other macropods and marsupials tested had 5% or less of the wallaroo level. The thermal denaturation profiles of the hybrids formed between cRNA (to the satellite) and DNA of species in the wallaroo group were identical; hybrids formed with DNA of other kangaroo species had a delta Tm of approximately 4 degrees C relative to the wallaroo. The chromosomal locations of the sequence in M. rufus and M. rufogriseus were in major blocks on the X chromosome, in association with the nucleolus organizer. The sequence also occurred at the centromere of the Y chromosome in M. rufogriseus, and in centromeric blocks on the four small acrocentric chromosomes of M. rufus which are believed to be related to metacentric chromosomes of 2n = 16 karyotypes by fusion or fission.