Congenital chromosome anomalies.

The introduction of chromosome banding techniques has led to the detection of a greatly increased number of congenital chromosome anomalies, especially those involving duplication and/or deficiency of short segments of chromosomes. Of most widespread use are the general banding techniques: Q-, G- and R-banding. Special staining methods provide help in certain cases. These include C-banding, G11 staining of some C-bands, Ag-staining of active ribosomal RNA gene clusters, differential staining of sister chromatids and differential staining of early or late replicating bands. Every banding method that can be produced by a fluorescent or nonfluorescent dye can be duplicated by the use of antinucleoside antibodies, providing strong support for the idea that the organization of DNA of particular nucleotide base composition and sequence is responsible for chromosome banding. As a result of the application of banding methods, a wealth of structural chromosmoe changes have been detected. In the balanced form, as translocations or inversions, these may have no effect on their carrier. However, such carriers have a markedly increased risk of having children with congenital chromosome anomalies. Most of these can be diagnosed prenatally using the generally available banding techniques.