The cells are grown in media for three days to two weeks depending on the sample source. Cell division is arrested during metaphase, when the chromosome material is condensed. Following hypotonic treatment and fixation, the cells are dropped on a slide and then stained. At least 20 metaphase spreads are analyzed and 2 or 3 metaphase spreads are photographed. The chromosomes are arranged to create a karyotype.
Chromosomes vary in size and in shape.
The sex chromosomes are placed to the right of the smallest autosomal chromosomes. Chromosomes vary in shape depending upon the position of the centromere, the structure that holds the two arms of the chromosomes together. If the centromere is in the middle, the chromosome is metacentric and the chromosome arms are equal in size. Normal female karyotype Chromosomes are further identified by banding patterns created by specialized staining procedures to produce G bands, R bands, C bands, etc. The choice of staining procedure depends upon the information that is desired.