Cytogenetics is the study of chromosomes and the related disease states caused by abnormal chromosome number and/or structure. Cytogenetics involves the study of human chromosomes in health and disease. Chromosome studies are an important laboratory diagnostic procedure in: • prenatal diagnosis, • certain patients with mental retardation and multiple birth defects, • patients with abnormal sexual development • some cases of infertility or multiple miscarriages. • the study and treatment of patients with malignancies and hematologic disorders. A variety of tissue types can be used to obtain chromosome preparations. Some examples include peripheral blood, bone marrow, amniotic fluid, and products of conception. Virtually all routine clinical Cytogenetic analyses are done on chromosome preparations that have been treated and stained to produce a banding pattern specific to each chromosome. This allows for the detection of subtle changes in chromosome structure. Although specific techniques differ according to the type of tissue used, the basic method for obtaining chromosome preparations is as follows: • Sample log-in and initial setup. • Tissue culture (feeding and maintaining cell cultures). • Addition of a mitotic inhibitor to arrest cells at metaphase. Harvest cells. This step is very important in obtaining high quality preparations. It involves exposing the cells to a hypotonic solution followed by a series of fixative solutions. This causes the cells to expand so the chromosomes will spread out and can be individually examined. Stain chromosome preparations to detect possible numerical and structural changes.The most common staining treatment is called Gbanding. A variety of other staining techniques are available to help identify specific abnormalities. Once stained metaphase chromosome preparations have been obtained they can be examined under the microscope. Typically 15-20 cells are scanned and counted with at least 5 cells being fully analyzed. During a full analysis each chromosome is critically compared band-for- band with it's homolog. It is necessary to examine this many cells in order to detect clinically significant mosaicism.