Isochore patterns

The third discovery was that isochore patterns showed phylogenetic differences. The most striking difference concerned the genomes of warm- and cold-blooded vertebrates. 

An important question concerns the effect of the minor shift on the isochore pattern. This problem has been explored on all syntenic regions shared by human and mouse, that were large enough to comprise more than one isochore. The results of this investigation (Pavli-cek et al., 2002b) indicate that the human isochore pattern is still recognizable in the mouse chromosomes after the minor shift. This will be illustrated here by considering the major histocompatibility (MHC) locus. 

Sabeur G., Macaya G., Kadi F., Bernardi G. (1993). The isochore patterns of mammalian genomes and their phylogenetic implications. J. Mol. Evol. 37 93-108. 

Portions of neutron powder diffraction patterns recorded on the high resoiution powder diffractometer (HRPD) instrument at ISIS (UK) from LaNis charged with deuterium in situ to approx. D/M = 0 to 0.6 in the a + p two-phase region. Dotted iine after muitipie pseudo-isobaric absorption steps. Soiid iine after a singie isochoric absorption step from D/M = 0. The iatter data are uninterpretabie except that they obviousiy represent regions of sampie with wideiy distributed iattice parameters. The highest peaks come from the aiuminium sampie ceii and demonstrate that the oniy difference between the two measurements is the state of the sampie. 

I- igurc 3.17. A. Isochore families from Xenopus. human, mouse and chicken, as deduced from density gradient centrifugation. B. Compositional patterns of coding sequences (represented by GCj values averaged per coding sequence) for Xenopus, mouse, chicken mid human. tModihed from Bernardi. 149.S). 

Figure 7.11. LI isochorc banding pattern. The left and riglit member of cacli chromosome pair shows the GTG (G bands by trypsin using Giemsa) bands and the LI is

Fig. 9.9 shows that the compositional patterns of chromosomes from Drosophila are characterized by a predominance of relatively GC-rich structures (corresponding to HI isochores) with very few GC-richer tracts but a relative abundance of GC-poor stretches (corresponding to L2 isochores). 

Caccio S., Jabbari K., Matassi G., Guermonprez F., Desgres J., Bernardi G. (1997). Methylation patterns in the isochores of vertebrate genomes. Gene 205 119-124... 

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