Oligonucleotide libraries useful for producing primers

An oligonucleotide library useful for producing an oligonucleotide of preselected sequence comprising a plurality of oligonucleotide members comprising one or more oligonucleotide species and having the compositional formula (X).sub.a (N).sub.b ;

• wherein X represents a non-degenerate nucleotide base and N represents a degenerate nucleotide base;
• "a" represents the number of non-degenerate nucleotide positions and is from 3 to 8;
• "b" represents the number of degenerate nucleotide positions and is from 0 to 4 but not greater than "a";
• and wherein each of said oligonucleotide species is capable of forming a hybridization complex with at least one other of said oligonucleotide species in said library, said hybridization complex having at least one unpaired nucleotide base overhang such that a single ligation event of said hybridization complex with another hybridization complex derived from said library having a complementary unpaired nucleotide base overhang produces a ligation reaction product comprising greater than 12 contiguous nucleotide base pairs.