A cDNA microarray ("Gene Chip"): measuring
variation in RNA expression
includes 1,046 different DNA oligonucleotides, each
specific for a particular cDNA sequence generated from
the mRNA transcriptome
of a particular tissue. The cDNAs
are fluorescently labelled and applied to the chip.
Quantitative patterns of gene activity are indicated by pseudocolours:
high levels of binding (and thus high levels of mRNA expression) are
indicated by "hot"
or "warm" signals,
while "cool" and "cold" signals indicate