Cytogenetics is a branch of biology focused on the study of chromosomes and their inheritance, especially as applied to medical genetics. Chromosomes are microscopic structures containing DNA that reside within the nucleus of a cell. During cell division, these structures become condensed and are visible with a microscope. Special staining techniques can be used to assess the number and structure of a person’s chromosomes as part of diagnostic testing. The number and/or structure of chromosomes is known to be altered in certain genetic diseases.
Cytogenetics is the term we use to discuss looking at the genetic material through a microscope. Traditionally this was done with a light microscope and looking at chromosomes. In fact, chromosomes were visible to those using microscopes even before we knew that they were made of DNA. In modern times we can use advanced cytogenetics techniques such as fluorescence in situ hybridization (FISH) to look at the genetic material in the cell through a light microscope but at much higher resolution.