Figure 5

Strategies for DNA sequencing. (a) Gain-of-hybridisation approach: an array is hybridised to normal DNA which has the base T at the position under interrogation or to test DNA containing a heterozygous T→G mutation. (b) Loss-of-hybridisation approach: in this example the array is hybridised to a mixture of normal DNA (solid bars) and DNA containing a mutation (open bars). The mutation is detected by its inability to hybridise at oligonucleotide positions that do hybridise to normal control DNA sequences. (c) Minisequencing: an array containing oligonucleotides attached at their 5' ends is hybridised to the target DNA and then incubated with a mixture of fluorescently tagged dideoxynucleoside triphosphates (ddNTP^*) and DNA polymerase. Covalent attachment of the tagged ddNTP^* is only possible if it complements the target sequence. (d) Universal array sequencing: the target sequence is hybridised to upstream LDR primers attached to 'zip code' sequences (Z1, Z2, etc) and to a downstream LDR primer containing a fluorescent tag. The two primers are only joined if the correct base pairing is present at the junction. (e) The ligated mixture is then hybridised to a universal array containing sequences complementing the 'zip codes'.