Abstract: The present invention relates to improved LCR amplification schemes using at least one downstream probe modified at its 5' end to reduce or eliminate target independent amplification. The different modified probes, and kits containing them are also presented. Also presented is a method for detecting differences in nucleic acid sequences, with reduced target independent amplification, using the modified probes.

Abstract: An improved, "gap filling" embodiment of the Ligase Chain Reaction (LCR) is described. Gap filling LCR is LCR wherein at least one of the probes is recessed so that a gap is formed between the adjacent probes when they are hybridized to target. The gap is filled using polymerase and deoxyribonucleotide triphosphates before ligation of the probes together. There are single and double gap versions, depending on whether one or two probes are recessed and require filling before ligation. The improvement resides in selecting and using target sequences such that only a single type, or two types, of deoxyribonucleotide triphosphate(s) are required to fill double gaps each being 1-10 bases in length, preferably 1-3 bases. Probes having specific sequences are claimed for a number of pathogens.