ABSTRACT
Some changes in chromosome morphology, detected during cytogenetic analysis, are not associated with clinical defects. Therefore a proper discrimination of harmless variants from true abnormalities, especially during prenatal diagnosis, is crucial to allow precise counselling. In this review we described chromosome variants and examples of chromosome anomalies that are considered to be unrelated to phenotypic consequences. The correlation between the presence of marker chromosomes and a risk of clinical signs is also discussed. Recently so-called molecular karyotyping, especially by the use of high-resolution array-CGH technique, contributed to revealing a high number of previously unknown small genomic variations, which seem to be asymptomatic, as they are present in phenotypically normal individuals