Genomic homogeneity is investigated for a broad base of DNA sequences in terms 
of dinucleotide relative abundance distances (abbreviated delta-distances) and 
of oligonucleotide compositional extremes. It is shown that delta-distances 
between different genomic sequences in the same species are low, only about 2 or 
3 times the distance found in random DNA, and are generally smaller than the 
between-species delta-distances. Extremes in short oligonucleotides include 
underrepresentation of TpA and overrepresentation of GpC in most temperate 
bacteriophage sequences; underrepresentation of CTAG in most eubacterial 
genomes; underrepresentation of GATC in most bacteriophage; CpG suppression in 
vertebrates, in all animal mitochondrial genomes, and in many thermophilic 
bacterial sequences; and overrepresentation of GpG/CpC in all animal 
mitochondrial sets and chloroplast genomes. Interpretations center on DNA 
structures (dinucleotide stacking energies, DNA curvature and superhelicity, 
nucleosome organization), context-dependent mutational events, methylation 
effects, and processes of replication and repair.