Compositional mapping based on physical maps

This result prompted a more detailed study of band Xq28 (De Sario et al., 1996), which was done by determining (De Sario et al., 1995) the buoyant densities (and GC levels) of 

Xq28 (De Sario et al., 1996) suggesting that YACs from isochore borders are unstable and/ or difficult to clone. Genes and CpG islands are very rare in the GC-poor region investigated, as expected from the fact that their concentration is proportional to the GC levels of the isochores in which they are contained. 

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