chromosome disorder

n. Any disorder caused by abnormality in the number or structure of the chromosomes. About 7-8% of all pregnancies are spontaneously aborted as a result of chromosome disorders in the developing fetus. Down syndrome, a form of mental retardation, is caused by abnormalities in chromosome 21; Turner's syndrome is caused by a partial or missing X, or female, chromosome; and some people inherit two Y, or male, sex chromosomes and are likely to have hypermasculine characteristics.