Figure 1. The GC-richest and GC-poorest human chromosomal bands. (a) The GC-richest bands. From left to right of each chromosome group: T, Chromomycin A3⁺/DAPI^– and H3⁺ bands (from Saccone and Bernardi, 2001). (b) The GC-poorest bands. The left and right member of each chromosome pair shows the Giemsa banding and the L1 isochore hybridization, respectively (from Federico et al., 2000). Biotinylated H3 and L1 isochores were detected with avidin-FITC and chromosomes were stained with propidium iodide. The H3 and the L1 isochores identify the gene-richest and the gene-poorest chromosomal regions, respectively. Note the different localization of the two isochore families, near the telomeres for H3 and more internal for L1 isochores.

Figure 2. H3⁺ bands at low and high chromosome resolution. Human chromosomes 19 and 22, at different levels of resolution, hybridized with the biotin-labelled DNA from the H3 isochore family. The hybridized regions were visualized by fluorescein and chromosomes were stained with propidium iodide. Both panels present chromosomes with a band resolution ranging from approximately 300 to approximately 850. The bands in chromosome 22 pointed by the red lines indicate the ribosomal DNA region (modified from Saccone et al., 1999).

Figure 3. H3⁺ and L1⁺ bands on human chromosome 11. Ideogram of human chromosome 11 at 400 (left) and 850 (right) band resolution showing the bands containing the gene-richest H3 and the gene-poorest L1 isochores. At 850 band resolution, the different degrees of darkness of G bands are also shown: note the correspondence among the L1⁺ bands and the darkest G bands (rightmost scheme). The R bands not containing H3 isochores are called H3^– bands, and the G bands not containing L1 isochores are called L1^– bands (modified from Saccone et al., 1999; Federico et al., 2000).