Once collected, these cells are placed in a nutrient-rich growth medium containing phytohemagglutinin (PHA), a substance that stimulates cell division. This solution causes the cells to swell, pushing the chromosomes apart from each other, which reduces overlap and improves resolution.
Karyotype Harvesting and Fixation: Collecting and Preparing Metaphase Chromosomes
This culturing period, which typically lasts 72 to 96 hours, is critical because chromosomes are only visible to the naked eye when the cell is actively preparing to divide. The drop is positioned just above a slide that has been slightly heated; as the droplet makes contact, the surface tension and heat cause the cells to rupture, spreading the chromosomes across the glass.
During metaphase, the chromosomes are maximally condensed and distinct from one another. Medical diagnostics and genetic research rely heavily on the ability to visualize an individual’s complete set of chromosomes, a process that begins with how a karyotype is prepared.
Optimizing Cell Culture and Harvest for Karyotype Slides
Step Two: Arresting the Cell Cycle To observe the chromosomes clearly, the cells must be halted at a specific stage of the cell cycle known as metaphase. In prenatal cases, amniotic fluid or chorionic villus sampling (CVS) is used to extract fetal cells.
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