Specimens are set up in a biologic safety cabinet. These cabinets
are designed to prevent specimen contamination, and to protect
the technologists from infectious disease. In this cabinet specimens
are mixed with culture media . They are then placed in a environmentally
controlled CO2 water-jacketed incubator. At this point, mitogens
may be added to specimens to encourage cell division. The amount
of time the specimens remain in the incubator varies depending
on tissue type and the type of study requested.
The next step in the procedure is the "harvesting"
of the cells. Harvesting is necessary to yield metaphase
spreads from the cells as they undergo mitosis. When
the specimen is ready to be harvested, Colcemid is
added to arrest the cells in the metaphase stage of
mitosis. This inhibits spindle fiber formation. By
inhibiting the spindle fibers from forming the chromatids
are not pulled apart and the chromosomes remain intact.
The Colcemid time and concentration depends on the
type of specimen being studied.
Interphase – DNA replicates- 2 double-stranded
Prophase – DNA condenses into chromosomes
Metaphase – Chromosomes are maximally condensed and
line up along the equatorial plate
Anaphase – Chromosomes are pulled apart into individual
Telophase – Two daughter cells are formed with exact
copies of the original DNA