Normal female karyotype

      Cytogenetics is the study of chromosome morphology, structure, pathology, function, and behavior. Chromosomes are best studied at mitotic or meiotic metaphase, although some studies, such as fluorescence in situ hybridization (FISH) methods, may utilize interphase cells. The metaphase chromosomes may be studied in spontaneously dividing tissues or in cells that have been stimulated to divide in culture.

Once dividing cells are obtained, mitotic arresting agents are used to collect the metaphase cells. Then the cells are processed (harvested). This is usually performed with suspensions of cells, although some cells are harvested “in situ” directly on the cultured cells in a Petri dish. During the harvest procedure, hypotonic solutions are used to increase cell volume, which spreads the chromosomes apart, and methanol-acetic acid is used to fix (preserve) them for study. Slides are prepared from fixed cells, either in suspension (dropped onto slides), or in situ, on the growth surface (fixed cells are allowed to dry on the flask, coverslip, or the slide on which they were cultured). Either way, cells are then stained with appropriate stains, observed, and analyzed. Computer-generated images are now used to arrange the chromosomes in pairs on karyograms.

The field has evolved to embrace molecular cytogenetic changes, now termed cytogenomics. Cytogeneticists utilize an assortment of procedures to investigate the full complement of chromosomes and/or a targeted region within a specific chromosome in metaphase or interphase. Tools include routine analysis of G-banded chromosomes that address specific chromosomal structures, and molecular probes, such as fluorescence in situ hybridization (FISH) and chromosome microarray analysis, which employ a variety of methods to highlight a region as small as a single, specific genetic sequence under investigation.

Arsham, M. S., Barch, M. J., & Lawce, H. J. (Eds.) (2017). The AGT Cytogenetics Laboratory Manual (4th Ed.). Hoboken, NJ: John Wiley & Sons, Inc.