The invention provides a method for diagnosis of genetic abnormalities or other genetic conditions which can be readily automated. The method is used to determine the presence or absence of a target sequence in a sample of denatured nucleic acid and entails hybridizing the sample with a probe complementary to a diagnostic portion of the target sequence (the diagnostic probe), and with a probe complementary to a nucleotide sequence contiguous with the diagnostic portion (the contiguous probe), under conditions wherein the diagnostic probe remains bound substantially only to the sample nucleic acid containing the target sequence. The diagnostic probe and contiguous probe are then covalently attached to yield a target probe which is complementary to the target sequence, and the probes which are not attached are removed. In the preferred mode, one of the probes is labeled so that the presence or absence of the target sequence can then be tested by melting the sample nucleic acid-target probe duplex, eluting the dissociated target probe, and testing for the label. In another embodiment, the testing is accomplished without first removing probes not covalently attached, by attaching a hook to the probe that is not labeled, so that the labeled target probe may be recovered by catching the hook.