Preparation of Metaphase Chromosomes for Analysis

Since chromosomes are visible as individual
structures under the light microscope only
during metaphase (or under special conditions
and for certain purposes, during prometaphase),
every chromosome analysis requires
dividing cells. In vivo, only bone marrow cells
contain a sufficient proportion of cells in mitosis.
Thus, in-vivo chromosome analysis of cells
is limited to bone marrow. All other procedures
for analyzing chromosomes in mitosis require
culturing of suitable cells (cell culture). Most
commonly, lymphocytes from blood are cultured
for chromosome preparations.
Peripheral blood lymphocytes stimulated by
phytohemagglutinin grow in a suspension culture.
Their life span is limited to a few cell divisions.
However, by exposing the culture to Epstein-
Barr virus they can be transformed into a
lymphoblastoid cell line with permanent
growth potential. Such cultures arewidely used
because they are much easier to handle than adhesion
cultures (p. 122).
In addition, fibroblasts from a piece of skin can
be propagated in cell culture for analysis (see
p. 122). However, since this procedure is somewhat
elaborate and time-consuming, it is used
only for certain purposes.