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Key Concepts

Under the microscope, after careful preparation and staining, chromosomes from dividing cells can be observed, photographed and arranged in pairs for close examination. This is called a karyotype.

    Key concepts:
  • It is usual to examine the chromosomes of somatic ("body") cells.
  • In humans 46 separate chromosomes can be seen in the karyotype.
  • Dividing cells (in humans these are usually white blood cells) are stopped in metaphase of mitosis by the addition of the drug colchicine.
  • Cells are swollen with water, fixed with alcohol on a glass slide and stained - often with florescent or other dyes.
  • A photograph of the stained chromosomes is taken (through a powerful microscope) and the individual chromosomes cut out and arranged in pairs.

Science@a Distance
© 2001, Professor John Blamire