Introduction

Chromosomes have captured the interest of scientists for well over 150 years. Initial studies of chromosomes were conducted in plants as early as the mid 1850s. At this time, technical limitations in microscopy and cytogenetic methodology precluded much advancement in the field. The first positive association between a chromosome aberration and a human disorder was made in 1959 when Lejeune and colleagues described trisomy 21 in nine cases of Down syndrome [2]. The first time that a characteristic chromosome change was associated with a specific neoplasm came in 1960 when Nowell and Hungerford identified an abnormally small G-group chromosome [the Philadelphia chromosome number 1 (Ph1)] in cells from patients with chronic myelogenous leukemia [3]. Prior to 1971, identification of each individual chromosome was limited to segregation into seven groups, A through G, using chromosome size and centromere placement as the identifiers. Individual identification of each chromosome was made possible in 1971 by methods developed by Caspersson and colleagues [4]. Using chemical treatment and nuclear dyes, patterns of dark and light areas or “bands” could be visualized along the length of each chromosome.