Which phase of cell division is most appropriate for chromosomal studies?

Chromosome preparations can be obtained from any actively dividing tissue by causing the cells to arrest in metaphase, the stage of the cell cycle when chromosomes are maximally condensed. Cells are isolated at metaphase or prometaphase and treated chemically or enzymatically to reveal chromosome "bands". Analysis of the number of chromosomes in the cell and the distribution of bands on individual chromosomes allow the identification of numerical or structural abnormalities. Ref: Schwaz S., Hassold T. (2012). Chapter 62. Chromosome Disorders. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.