Humans have 23 pairs of chromosomes, i.e., one pair of sex chromosomes (X and/or Y) and 22 pairs of autosomes (chromosomes 1-22). Many human genetic disorders result from unbalanced chromosome abnormalities, in which there is a net gain or loss of genetic material. Numeric and structural chromosomal abnormalities occur in approximately 0.6% of live births,1 and often result in dysmorphism, malformations, and/or developmental disabilities. The resulting phenotypes are caused by the imbalance of one or more dosage-sensitive genes in a particular chromosome or chromosomal segment. Such gene...

Some of the abnormalities associated with chromosome structure and number can be detected by karyotype. A karyotype can show prospective parents whether they have certain abnormalities that could be passed on to their offspring, or it may be used to learn the cause of a child's disability. karyotypes can also reveal the gender of a fetus or test for certain defects through examination of cells from uterine fluid - a procedure called amniocentesis - or through sampling of placental membranes. Over 400,000 karyotype analyses are performed each year in the U.S. and Canada.To create a karyotype,...