Thee term "cytogenetics", a combination of cytology and genetics, was first introduced by
Suttonn in 1903. Only few studies on human cytogenetics were published until the fifties, and
accuratee studies on human chromosomes became only possible after several technical
developments.. Taking advantage of improvements in cell culturing and chromosome
spreading,, Tjio and Levan (1956) were able to demonstrate that the human diploid
chromosomee number is 46. Purely on morphological criteria the 23 chromosome pairs could
bee classified in seven groups (A-G), as originally suggested by Patau (1960). A system for
nomenclature,, using this classification, was proposed at what became known as the "Denver
Conferencee of 1960" and was officially sanctioned by the "London Conference" in 1963
(ISCN,, 1995). In 1959 the first aberration was reported: Lejeune et al. (1959) discovered an
extraa chromosome (belonging to the G-group) to be present in patients with Down syndrome.
Thiss was soon followed by the description of a number of syndromes involving the sex
chromosomes.. In 1960 two more autosomal trisomies were reported. Patau et al. (1960)
describedd a trisomy with an extra D-group chromosome, while Edwards et al. (1960) described aa patient with a trisomy for an E-group chromosome.
AA major advance was the observation of Caspersson et al. (1968) of a kind of banding pattern, whenn staining plant chromosomes with fluorescent quinacrine compounds. This resulted in twoo articles by Caspersson et al. (1970% 1971) in which it was shown that such a staining producedd consistent fluorescent banding patterns (Q-bands) along each human chromosome.
Thiss unique banding pattern made possible the identification of all human chromosomes.
Otherr banding techniques soon followed, utilizing either fluorescent dyes or the Giemsa stain resultingg in G-bands (Drets and Shaw, 1971). A basic system for designating not only
individuall chromosomes, but also chromosome regions and bands was proposed in a report of thee "Paris Conference" of 1971. With revisions during the years this system has become a widelyy accepted nomenclature for human chromosomes (ISCN, 1995). By using this banding phenomenon,, Patau syndrome proved to be a trisomy 13 and Edwards syndrome was seen to bee a trisomy 18. With this technique of differential staining one could distinguish chromosome 211 from the other G-group chromosome (chromosome 22) and recognise different segments onn chromosome 21. Caspersson et al. (1970b
) formulated the following: "this implies that the geneticc material, which in triplicate gives Down's syndrome, is on the distal part on the long armm of chromosome 21" . In this way, many more chromosomal abnormalities and syndromes couldd be identified.