Cytogenetics is the branch of genetics that studies the structure of DNA within the cell nucleus. This DNA is condensed during cell division and form chromosomes. The cytogenetic studies the number and morphology of chromosomes. Using chromosome banding techniques (classical cytogenetics) or hybridization fluorescently labeled probes (molecular cytogenetics). The number and morphology of chromosomes in a cell of a particular species are always constant, in most cells of the body (with the exception of reproductive cells and others such as the liver). This is a characteristic of each specie, in humans such as the number of chromosomes is 46.
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.- Amalia S. Dutra, Ph.D.