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Human genetics is a discipline, which includes pre- and post-natal counseling of patients and families. A genetic basis can be considered in individuals suffering from infertility and/or repeated abortions, or any kind of acquired or inherited syndrome [1]. At present, genetic counselors have a multitude of technical possibilities, some highly sophisticated, for the genetic analysis of an individual. Approaches such as next-generation sequencing of a whole genome has gained importance and has been helpful on many occasions [1,2].
Besides genetic counseling, another key element of human genetics is still the well-established approach of cytogenetics, including molecular cytogenetics [1]. In many western countries (e.g., Germany), insurance companies request, where appropriate, banding cytogenetics as the starting test for a genetic analysis. Thus, up to 40% of individuals in search of advice are still studied cytogenetically, and a subset of them are further analyzed by molecular cytogenetics [Schreyer I, Pers. Comm .]. Additionally, in most countries (except for North America and western Europe) cytogenetics is still the gold standard for any genetic analysis, with molecular cytogenetics becoming available over the last decade.
After the introduction of array-comparative genomic hybridization (aCGH), cytogenetics/molecular cytogenetics were considered to be outdated by some researchers [3,4]. However, it is common knowledge that aCGH results can only be correctly interpreted if cytogenetics is performed in parallel; in addition, abnormal aCGH results need to be confirmed by a second method, such as molecular cytogenetics [5,6].
Molecular cytogenetics
In banding cytogenetics - today often incorrectly called 'classical cytogenetics'(classical cytogenetics is Giemsa or Orcein staining without any banding) - only chromosome morphology combined with a black and white banding pattern is evaluated. Thus, only changes within the normal banding pattern, size variations in a chromosomal band or the chromosome itself, and changes to the centromere index, can be detected [7]. To overcome these limitations, FISH approaches were introduced in the 1980s, and the new field of 'molecular cytogenetics'was launched. For more information on FISH, readers are directed to [8], as such a discussion will not be covered in this review.
One-, two- and three-color FISH experiments are standard in every laboratory around the world performing molecular cytogenetics. Multicolor FISH (mFISH) is defined as the simultaneous use of at least three different ligands or fluorochromes for the...