Isochores and Chromosomal Bands

Giorgio Bernardi
Stazione Zoologica Anton Dohrn
Villa Comunale
80121 Napoli Italy
telephone: 0039 081 5833 300/402
fax: 0039 081 2455807
prestype: Platform
presenter: Giorgio Bernardi

S. Saccone1,2, A. Pavlicek3, C. Federico1 and G. Bernardi4

1Dipartimento di Biologia Animale, University of Catania, via Androne 81, 95124 Catania, Italy;
2Dipartimento di Protezione e Valorizzazione Agroalimentare, University of Bologna, via F.lli Rosselli 107, 42100 Reggio Emilia, Italy;
3Institute of Molecular Genetics, Czech Academy of Sciences - Flemingovo nam. 2 - 166 37 Prague 6, Czech Republic
4Laboratorio di Evoluzione Molecolare, Stazione Zoologica, Villa Comunale, 80121 Napoli, Italy; Tel: (+39) 081 5833300; Fax: (+39) 081 2455807; E-mail:

The human genome is formed by isochores belonging to five families, L1, L2, H1, H2, and H3, that are characterized by increasing GC levels and gene concentrations. In situ hybridization of DNA from different isochore families, provides, therefore, information not only on the correlation between isochores and chromosomal bands, but also on the distribution of genes in chromosomes. Three subsets of R(everse) bands, H3+, H3* and H3­, that contain large, moderate, and no detectable amounts, respectively, of the gene- richest H2 and H3 isochores, and replicate very early and early, respectively, in S phase of the cell cycle, were identified.

Recent investigations on the GC levels, replication timings and DNA compaction of G (iemsa) bands, showed that G bands comprise two different subsets of bands, one of which is predominantly composed of L1 isochores, replicates at the end of the S phase, has a higher DNA compaction relative to H3+ bands and corresponds to the darkest G bands of Francke (Cytogenet. Cell Genet. 6: 206-219, 1994). In contrast, the other subset is composed of L2 and H1 isochores, has less extreme properties in replication and composition and corresponds to the less dark G bands of Francke.

Finally, the correlation between base composition of DNA and chromosomal bands as investigated using the DNA sequences of chromosomes 21 and 22 will be reported.

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