Fig. 2: Schematic of a DNA microarray. (A) A mixture of DNA or RNA from a diagnostic sample is labelled with a fluorescent probe and layered onto a chip. (B) The chip consists of a solid support spotted in a grid pattern with thousands to tens of thousands of different single-stranded DNA sequences. (C) During incubation under carefully chosen conditions, only sequences complementary to each individual probe bind to that spot on the array. (D) When the array is read, the pattern of fluorescence indicates the sequences present in the sample and their quantities. Photo: Alison Sinclair