High resolution banding present aspects

Mammalian chromosomes can be defined by three structural classes visualized as the G/(a-bands, the R-bands, and the C-bands, which are associated with different functional and biochemical attributes. This chromosomal prepattern has developed during vertebrate evolution and determines the kind and quality of banding which can be obtained from different vertebrate taxa (Holmquist, 1989). The vertebrate genome is organized in very long DNA sequences of homologue base composition called isochores (Bernardi, 1989). During evolution, mammals and birds have sep-arated from reptiles and lower vertebrates with regard to distribution and base composition of the isochores. This difference, which is reflected in the chromoso-mal prepattern, indicates that isochores are evolutionary units of the vertebrate genome (Bernardi, 1989). In mammals and birds, the genome can be divided into two subgenomes, the first one, the paleogenome, has not changed during vertebrate evolution. It is composed of late replicating dG-dC-poor isochores. It contains the long interspersed repeated DNA-sequences (LINES) and the tissue-specific genes (Holmquist, 1989). It corresponds to the late replicated G-band chromatin of early