title: Structural variability of human chromosome 9 in relation to its evolution.
abstract: Human chromosome 9 shows a high susceptibility for structural rearrangements, particularly pericentric inversions, which often are transmitted. Three types of pericentric inversions can be observed on No. 9: 1) Type I, showing the total constitutive heterochromatin in the short arm. 2) Type II with part of the C heterochromatin on the short arm, the rest located on the long arm proximal to the centromere. 3) Type III: a subtelocentric chromosome with part of the C heterochromatin in the very short arm and the rest located interstitially on the long arm. With these inversions as well as with other structural rearrangements, e.g. translocations, the break-points are located preferentially within the C heterochromatin or close to the heterochromatic-euchromatic junctions. These findings are in contrast to the findings in lymphocytes from 5 patients with fancomi's and after irradiation in vitro, reported in the literature. In lymphocytes break-points seem to be distributed more or less by chance. These observations together led us to speculate that human chromosome 9 primarily was an acrocentric chrosome; in morphology and at least in some functions similar to D- and G-group chromosomes. During evolution this acrocentric chromsome changed to a submetacentric one due to a pericentric inversion.
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002869:Chromosome Aberrations; D002872:Chromosome Deletion; D007446:Chromosome Inversion; D002875:Chromosomes / Q000528:radiation effects; D002906:Chromosomes, Human, 6-12 and X; D005199:Fanconi Anemia / Q000235:genetics; D006570:Heterochromatin / Q000032:analysis; D006801:Humans; D011323:Primates; D011831:Radiation Genetics; D012730:Sex Chromosomes; D014178:Translocation, Genetic
chemical_list: D006570:Heterochromatin