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Small supernumerary marker chromosomes (SMCs) are present in about 0.05% of the human population. In approximately 30% of SMC carriers (excluding the approximately 60% SMC derived from one of the acrocentric chromosomes), an abnormal phenotype is observed. The clinical outcome of an SMC is difficult to predict as they can have different phenotypic consequences because of (1). differences in euchromatic DNA-content, (2). different degrees of mosaicism, and/or (3). uniparental disomy (UPD) of the chromosomes homologous to the SMC. Here, we present 35 SMCs, which are derived from all human chromosomes, apart from chromosome 6, as demonstrated by the appropriate molecular cytogenetic approaches, such as centromere-specific multicolor fluoresence in situ hybridization (cenM-FISH), multicolor banding (MCB), and subcentromere-specific multicolor FISH (subcenM-FISH). In nine cases without an aberrant phenotype, neither partial proximal trisomies nor UPD could be detected. Abnormal clinical findings, such as psychomotoric retardation and/or craniofacial dysmorphisms, were associated with seven of the cases in which subcentromeric single-copy probes were proven to be present in three copies. Conversely, in eight cases with a normal phenotype, proximal euchromatic material was detected as partial trisomy. UPD was studied in 12 cases and subsequently detected in two of the cases with SMC (partial UPD 4p and maternal UPD 22 in a der(22)-syndrome patient), indicating that SMC carriers have an enhanced risk for UPD. At present, small proximal trisomies of 1p, 1q, 2p, 6p, 6q, 7q, 9p, and 12q seem to lead to clinical manifestations, whereas partial proximal trisomies of 2q, 3p, 3q, 5q, 7p, 8p, 17p, and 18p may not be associated with significant clinical symptoms. With respect to clinical outcome, a classification of SMCs is proposed that considers molecular genetic and molecular cytogenetic characteristics as demonstrated by presently available methods.

Background: Nuclear architecture studies in human sperm are sparse. By now performed ones were practically all done on flattened nuclei. Thus, studies close at the in vivo state of sperm, i.e. on three-dimensionally conserved interphase cells, are lacking by now. Only the position of 14 chromosomes in human sperm was studied.

The origin of the human and great ape chromosomes has been studied by comparative chromosome banding analysis and, more recently, by fluorescence in situ hybridization (FISH), using human whole-chromosome painting probes. It is not always possible, however, to determine the exact breakpoints and distribution or orientation of specific DNA regions using these techniques. To overcome this problem, the recently developed multicolor banding (MCB) probe set for all human chromosomes was applied in the present study to reanalyze the chromosomes of Gorilla gorilla (GGO). While the results agree with those of most previous banding and FISH studies, the breakpoints for the pericentric inversion on GGO 3 were defined more precisely. Moreover, no paracentric inversion was found on GGO 14, and no pericentric inversions could be demonstrated on GGO 16 or 17.

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Background: Even though comparative nuclear architecture studies in hominoids are sparse, nuclear chromosome architecture was shown to be conserved during hominoid evolution. Thus, it is suspected that yet unknown biological mechanisms must underlie this observation.