Chromosomal analysis

Chromosomal analysis is usually performed on white blood cell
cultures. Other samples analysed on a routine basis include
cultures of fibroblasts from skin biopsy samples, chorionic villi
and amniocytes for prenatal diagnosis, and actively dividing
bone marrow cells. The cell cultures are treated to arrest
growth during metaphase or prometaphase when the
chromosomes are visible. Until the 1970s, chromosomes could
only be analysed on the basis of size and number. A variety of
banding techniques are now possible and allow more precise
identification of chromosomal rearrangements. The most
commonly used is G-banding, in which the chromosomes are
subjected to controlled trypsin digestion and stained with
Giemsa to produce a specific pattern of light and dark bands
for each chromosome.