Molecular Approaches for Delineating Marker Chromosomes

A marker chromosome is defined as a structurally abnormal supernumerary chromosome that can not be identified by routine cytogenetics. Examples of marker chromosomes include rings, derivatives, dicentrics, and minute chromosomes. Current literature suggests that supernumerary marker chromosomes are found in 0.14–0.72/ 1000 newborns and more commonly in prenatal testing at 0.65–1.5/1000 (1 ). The significance of a marker chromosome depends on several factors, including inheritance, mode of ascertainment, chromosomal origin, and morphology as well as structure of the marker.