Gene expression profile by cDNA array

This figure shows amicroarray of 1500 different
cDNAs from the human X chromosome. The
cDNAs were obtained from lymphoblastoid
cells of a normal male (XY) and a normal female
(XX). The cDNAs of the male cells were labeled
with the fluorochrome Cy3 (green) and the
cDNAs of the female cellswere labeledwith Cy5
(red). The inactivation of most genes in one of
the two X chromosomes in female cells leads to
a 1:1 ratio of cDNAs from the expressed genes
in the male and the female X chromosomes
(yellowsignal at most sites because red fluorescence
(female) and green fluorescence (male)
signals are superimposed owing to the similar
expression levels in male and female cells). An
exception is the XIST gene, which regulates X inactivation
(see p. 228). It is expressed on the inactive
X chromosome only.