Chromosomal anomalies cause various disorders. Anomalies that affect autosomes (the 22 paired chromosomes that are alike in males and females) are more common than those that affect sex chromosomes (X and Y).
Chromosomal abnormalities fit into several categories but broadly may be considered as numerical or structural.
Numerical abnormalities include
Structural abnormalities include
Some specific terms from the field of genetics are important for describing chromosomal anomalies:
Lymphocytes are typically used for chromosomal analysis, except prenatally, when amniocytes or cells from placental chorionic villi are used (see Amniocentesis). Recently, free fetal DNA obtained from a maternal blood sample has been used for prenatal diagnosis of trisomy 21 (Down syndrome). A karyotype analysis involves blocking cells in mitosis during metaphase and staining the condensed chromosomes. Chromosomes from single cells are photographed, and their images are arranged, forming a karyotype.
Several techniques are used to better delineate the chromosomes:
Last full review/revision December 2012 by Nina N. Powell-Hamilton, MD
Content last modified September 2013