Cytogenetics is a branch of pathology and genetics concerned with the study of normal chromosomes and chromosome aberrations. Classical cytogenetics allows microscopic visualization of whole chromosomes in order to assess their number and structure. Molecular cytogenetics uses specialized techniques such as fluorescence in situ hybridization (FISH) and array comparative genomic hybridization (aCGH) to evaluate submicroscopic chromosomal regions. Both classical and molecular cytogenetic techniques are used to investigate constitutional and acquired chromosome abnormalities. Most recently, next-generation sequencing has been added to the cytogenetic lab arsenal, to allow exact identification of breakpoints in chromosome rearrangements. Each of these techniques will be discussed in more detail in subsequent sections,The study of chromosomes, which are long strands of DNA and protein that contain most of the genetic information in a cell. Cytogenetics involves testing samples of tissue, blood, or bone marrow in a laboratory to look for changes in chromosomes, including broken, missing, rearranged, or extra chromosomes. Changes in certain chromosomes may be a sign of a genetic disease or condition or some types of cancer. Cytogenetics may be used to help diagnose a disease or condition, plan treatment, or find out how well treatment is working.