Metaphase

Metaphase is the time period during eukaryotic cell division in which chromosomes line up along the equatorial plane of the cell before being drawn apart to opposite poles of the cell. Metaphase occurs once during mitosis but twice during meiosis (in meiosis these phases are called metaphase I and metaphase II). Metaphase is preceeded by Prometaphase and followed by Anaphase. Because metaphase chromosomes are highly condensed, scientists use these chromosomes for gene mapping and identifying chromosomal aberrations.

Sources

http://www.genome.gov/glossary.cfm?key=metaphase