Patent ID: 6924103

Claim:
A DNA array substrate for screening variation in a portion of a nucleic acid comprising: a first group of probes, each probe having a base sequence that hybridizes with a wild-type sequence of the portion to give a strong signal, and a second group of probes, each probe having a base sequence that is expected to hybridize with a gene variant but not with the wild-type sequence to give a strong signal; wherein each probe is fixed as a separate probe spot on a substrate to form at least two separate regions of probe spots selected from: a first region containing probes of the first group, a second region containing probes of the second group, each of which provides a weaker signal than the probes of the first region on reaction with the wild-type sequence, and a third region containing probes of the second group, each of which provides no signal on reaction with the wild-type sequence, wherein the probe spots are grouped such that each one of the regions contains probes not found in other regions.