Karyotyping is a valuable research tool used to determine the chromosome
complement within cultured cells. It is important to keep in mind that karyotypes
evolve with continued culture. Because of this evolution, it is important for the
interpretation of biochemical or other data, that the karyotype of a specific
subline be determined. Numerous different technical procedures have been
reported that produce banding patterns on metaphase chromosomes. A band is
defined as the part of a chromosome that is clearly distinguishable from its
adjacent segments by appearing darker or lighter. The chromosomes are
visualized as consisting of a continuous series of light and dark bands. A Gstaining
method resulting in G-bands uses a Giemsa or Leishman dye mixture
as the staining agent. What follows is a brief description of the steps involved
in assembling a karyotype.
15–30 minutes to cut, arrange, glue and interpret 1 metaphase spread on a
- Count the number of chromosomes. Solid-stained chromosomes or
chromosomes treated with a trypsin and giemsa stain can be counted at
the microscope with a 100X magnification. However, for analysis such as
identification of marker chromosomes or determination of the number of
copies of individual chromosomes, it is usually necessary to photograph
and print the chromosome spreads. Refer to procedures in this manual for
black and white photography and film development. Two prints should be
made of each spread. One will be cut for karyotyping; the uncut print
serves as a reference if questions arise about the interpretation of a certain
- Cut out each individual chromosome and arrange on a karyotype sheet.
Chromosomes are ordered by their length, the position of the centromere,
the position of the chromosome bands, and the relative band sizes and
- In the construction of the karyotype, the autosomes are numbered 1 to 22,
in descending order of length. The sex chromosomes are referred to as X
and Y. The symbols p and q are used to designate, respectively, the short
and long arms of each chromosome. There are 7 groups identified in the
karyotype, and data pertaining to each group.
- Secure chromosomes in place with glue. Pair the chromosomes closely
together and align the centromeres (for easier band comparison and
checking for structural chromosome aberrations). If possible, have a second
technologist check the interpretation of the karyotype before chromosomes
are secured in place.
- A description of the karyotype should be recorded on the karyotype sheet.
First record the number of chromosomes, including the sex chromosomes,
followed by a comma (,). The sex chromosome constitution is given next.
Any structural rearrangements and additional or missing chromosomes
are listed next. Other information such as the cell line number, the date
karyotype was prepared, the specimen type, and the technologist should
also be recorded on the karyotype sheet.