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Chromosomes are the long stretches of DNA that contain our genes. "Cytogenetics" is a word used to describe the study of chromosomes. The chromosomes need to be stained in order to see them with a microscope. When stained, the chromosomes look like strings with light and dark "bands." A picture (an actual photograph from one cell) of all 46 chromosomes, in their pairs, is called a "karyotype." A normal female karyotype is written 46, XX, and a normal male karyotype is written 46, XY.
The standard analysis of the chromosomal material evaluates both the number and structure of the chromosomes, with an accuracy of over 99.9%. Chromosome analyses are usually performed using a blood sample (white blood cells), prenatal specimen, skin biopsy, or other tissue sample.
Chromosomes are analyzed by specially trained healthcare personnel that have advanced degrees in cytogenetic technology and genetics. Chromosome studies may be performed when a child is born with multiple birth defects.
Chromosome studies may also be performed when people have certain types of leukemias and lymphomas, to look for specific chromosome rearrangements (changes in the order of the chromosome material) associated with these types of cancers.