Classical satellites I, II and III are composed of a mixture of repeated sequences. However, each of them contains a simple family of repeated sequences as a major component. Satellites 2 and 3 are simple families of repeated sequences that form the bulk of human classical satellites II and III, respectively, and are composed of closely related sequences based on tandem repeats of the pentamer ATTCC. For this reason, extensive cross-hybridizations are probably responsible for the similar in situ hybridization patterns obtained for satellites II and III. We have used a fluorescent in situ hybridization method with highly specific oligonucleotides for satellites 2 and 3, respectively, as probes. Our results show that satellite 2 is mainly located on chromosomes 1, 2, 10 and 16, whereas the major domain of satellite 3 is on chromosome 9. Furthermore, minor sites of satellites 2 and 3 are shown. Two-colour in situ hybridizations have enabled us to define the spatial relationships existing between the major domains of both satellites and centromeric alpha satellite sequences. These experiments indicate that the heterochromatin regions of chromosomes 1, 9 and 16 have different molecular organizations.

The variant allele of the C677T has a protective effect on CRC development, whereas the variant allele of the A1298C does not produce any effect on disease risk. Both MTHFR polymorphisms are relevant and independent factors of patient outcome after 5FU-based treatment of CRC, and MTHFR genotyping may be of predictive benefit in selecting treatment regimens.

The current results suggested that c.3618A>G polymorphism in COX2 is a good prognostic indicator for patients with CRC. Genotyping this polymorphism may be useful for predicting the clinical outcome of sporadic CRC.

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We have used a fluorescent in situ hybridization procedure to detect human satellite 1 DNA, the simple sequence family that constitutes the non-male-specific fraction of classical satellite 1 DNA. Satellite 1 appears to be located on pericentromeric regions of chromosomes 3, 4 and 13, and on satellites of each acrocentric chromosome. These results suggest a possible relationship between quinacrine fluorescence of heterochromatin and DNA composition. Furthermore, by means of multicolour in situ hybridization, we have spatially resolved satellite 1 sequences and centromeric alpha-satellite within heterochromatic blocks.