High resolution banding

High-resolution banding: present aspects
M Rønne
Institute

Odense

of Medical Biology, Department of Anatomy and Cytology, University, Campusvej 55, 17K-5230 Odense M, Denmark European Colloquium on Cytogenetics of Toulouse-Auzeville, 10-13 July 1990)
Domestic

(Proceedings

of the 9th

Animals;

high resolution/ R-banding/ G-banding
EVOLUTIONARY 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 separated from reptiles and lower vertebrates with regard to distribution and base composition of the isochores. This difference, which is reflected in the chromosomal 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 earlycondensating chromomeres and is subjected to lyonization during embryonic development (Holmquist, 1989). The second one, the neogenome, has changed from the ancestral early replicating dG-dC-poor isochores of late-condensating interchromomeres into the early-replicating compositionally heterogeneous dG-dC-rich isochores of late-condensating interchromomeric chromatin. This subgenome contains the short interspersed