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The karyotype is the set of 46 chromosomes. Karyotyping is the analysis which checks for the correct number and structure of all the chromosomes. A sample of amniotic fluid or chorionc villi is collected and sent to the laboratory. There the sample is cleaned and placed in a culture medium. They are kept at body temperature so that they can divide and multiply.

This can take 5-8 days. Once they are ready to be examined their growth is stopped at a point in the division cycle where the chromosomes are clearly visible. This is called the “metaphase”. The cells are then stained so that the patterns on each chromosome can be identified. The cytogeneticist analyses the chromosomes down the microscope using state-of-the-art computer imaging. The chromosomes are examined to make sure that no bits are missing and that no material is extra.

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